Another suggestion is that it was made in the Carolingian period. We know that Charlemagne had a bronze group of the Lupercalia, now lost, outside the palace he had built in Aachen - he called it the Lateran Palace and it copied the one in Rome, as part of Charlemagne's propaganda that he was the new Constantine. Literary sources indicate that he had the Aachen Lupercalia brought not from Rome but from a site in southern Gaul.
The problem is that bronze statues tended to be melted down so that the metal could be re-used, and the next large hollow cast statue we have after antiquity is the Lion of Brunswick around 1166. Although there are some minor superficial similarities between the lion and the Lupercalia, this is probably because the German artist was attempting to copy an ancient image.
Since the most obvious theory is often the correct one, I prefer for now to assume that the surviving bronze Lupercalia is an ancient one, whose legs were repaired. Assuming it is an original work of the late 6th century BC, Roman artists were still too unsophisticated to produce such a work, so we can assume that an Etruscan sculptor created it. The original temple of Jupiter Optimus on the Capitoline hill was built at the end of the 6th century BC employing Etruscan artists (Volcanius of Veii worked on the sculpture according to Pliny, NH 35.45) and dedicated in 509 BC.
There were also a couple of Etruscan images showing such scenes.
A wolf or lion suckled a single child was carved on the 5th or 4th century BC Bologna Stele - ancient Felsina remained independent of Rome until the Battle of Telamon (225 BC), although it was not purely Etruscan since the Boii tribe had settled there around the time of their invasion of Rome in 390 BC. Before that the city was purely Etruscan and possibly named Velzna, and that is when this funerary stele was created.
There were trade links between Crete and Italy from the Mycenean period onwards, and Miletus was not only a great coloniser but a leading trading state - Herodotus 6.21 speaks of a trade agreement between Miletus and Sybaris (c. 600 BC; see also Athenaeus 519B). Herodotus of course controversially claimed that the Lydians had colonised "Tyrrhenia" or Etruria (1.94). This is not to assume a Cretan or Ionian origin for the motif at Bologna, but merely to emphasise that there was a great deal of trade between the regions at the time.
Another scene, on a mirror said to have been found at Bolsena shows two children being suckled by a wolf:
A similar scene can be found on the cast foot of the 4th century Ficoroni cista, found in the grave of a woman at Praeneste, but made in Rome for her according to the inscription: "NOVIOS PLVTIUS MED ROMAI FECID/ DINDIA MACOLNIA FILEAI DEDIT" ... Whether the Bolsena Mirror shows Romulus and Remus or an Etruscan myth is still debated by scholars. It was made in the 4th century BC, so would in any case post-date the Capitoline Lupercalia, and would the Bologna Stele, so neither could have influenced it. If the Ficus Navia Lupercalia of 296 BC had been the first Roman Lupercalia, it could have been influenced by the Etruscan scenes but ...
What the images do indicate is that there were many ancient myths and stories where a child was the victim of exposure, but was rescued, sometimes by animals, grew up to be a hero, etc - and that the Etruscans may have had such a myth. Silvius was raised by shepherds and animals, as was Caeculus of Praeneste (Servius, Aeneid, 7, 678).
As I've noted before, the eponymous founders of Miletus and Cydonia were, according to their local myths, also suckled by a wolf and a bitch (here). Cyrus the Great was said to have been suckled by a bitch, Aegisthus by a goat (Aelian, Varia Historia 12. 42; Hyginus, Fabulae 87, 88 & 257), Paris of Troy by a bear; Aeolus and Boeotus by a cow or dogs (Ovid. Heroides, 11; Hyginus. Fabulae, 238, 242); Antilochus by a dog (Hyginus Fabulae 252); Asclepius by a goat; and the list goes on ... Exposure was probably common, and the myths developed not only to emphasise the rise from nothing of the heroes but also as a way of dealing with exposure as an issue by creating myths of salvation. There have been numerous reports in the modern period of abandoned babies raised by animals, but most have turned out to be hoaxes.
The image of a boy being suckled by an animal was nothing new. But then nor was the image of Aeneas carrying Anchises, which had been on the coins of Macedonian Aeneia from the Archaic period onwards (source):
And the idea of Trojans fleeing to Italy was not unique to the history of Rome. Stesichorus of Himera in the 6th century wrote of Trojans at Hesperia (whose location is unknown now), though not of Aeneas (JSTOR). By the fifth century it had become part of standard Sicilian myth, recorded by Thucydides (6.2.3-4):
On the fall of Ilium, some of the Trojans escaped from the Achaeans, came in ships to Sicily, and settled next to the Sicanians under the general name of Elymaeans; their towns being called Eryx and Segesta. With them settled some of the Phocians carried on their way from Troy by a storm, first to Libya, and afterwards from thence to Sicily.Aeneas became a central figure in this migration during the 1st century BC, later claimed to be the founder of Segesta (Cicero, Verres), and honoured in Sicily according to Dionysius of Halicarnassus Roman Antiquities I. 53,1:
There are many proofs of the coming of Aeneas and the Trojans to Sicily, but the most notable are the altar of Aphroditê Aeneias erected on the summit of Elymus and a temple erected to Aeneas in Aegesta; the former was built by Aeneas himself in his mother's honour, but the temple was an offering made by those of the expedition who remained behind to the memory of their deliverer. The Trojans with Elymus and Aegestus, then, remained in these parts and continued to be called Elymians; for Elymus was the first in dignity, as being of the royal family, and from him they all took their name.Some of the stories told about how Rome was founded are gathered by Dionysius of Halicarnassus Roman Antiquities I. 72:
But as there is great dispute concerning both the time of the building of the city and the founders of it, I have thought it incumbent on me also not to give merely a cursory account of these things, as if they were universally agreed on. For Cephalon of Gergis, a very ancient writer, says that the city was built in the second generation after the Trojan war by those who had escaped from Troy with Aeneas, and he names as the founder of it Romus, who was the leader of the colony and one of Aeneas' sons; he adds that Aeneas had four sons, Ascanius, Euryleon, Romulus and Remus. And Demagoras, Agathyllus and many others agree with him as regards both the time and the leader of the colony.
But the author of the history of the priestesses at Argos and of what happened in the days of each of them says that Aeneas came into Italy from the land of the Molossians with Odysseus and became the founder of the city, which he named after Romê, one of the Trojan women. He says that this woman, growing weary with wandering, stirred up the other Trojan women and together with them set fire to the ships. And Damastes of Sigeum and some others agree with him.
But Aristotle, the philosopher, relates that some of the Achaeans, while they were doubling Cape Malea on their return from Troy, were overtaken by a violent storm, and being for some time driven out of their course by the winds, wandered over many parts of the sea, till at last they came to this place in the land of the Opicans which is called Latinium, lying on the Tyrrhenian sea.
And being pleased with the sight of land, they hauled up their ships, stayed there the winter season, and were preparing to sail at the beginning of spring; but when their ships were set on fire in the night and they were unable to sail away, they were compelled against their will to fix their abode in the place where they had landed. This fate, he says, was brought upon them by the captive women they were carrying with them from Troy, who burned the ships, fearing that the Achaeans in returning home would carry them into slavery.
Callias, who wrote of the deeds of Agathocles, says that Rhome, one of the Trojan women who came into Italy with the other Trojans, married Latinus, the king of the Aborigines, by whom she had three son, Romus, Romulus and Telegonus . . . and having built a city, gave it the name of their mother. Xenagoras, the historian, writes that Odysseus and Circê had three sons, Romus, Anteias and Ardeias, who built three cities and called them after their own names.
Dionysius of Chalcis names Romus as the founder of the city, but says that according to some this man was the son of Ascanius, and according to others the son of Emathion. There are others who declare that Rome was built by Romus, the son of Italus and Leucaria, the daughter of Latinus.The "author of the history of the priestesses at Argos" was Hellanicus of Mytilene; he and Damastes of Sigeum wrote towards the end of the 5th century, when Rome was still a village whose only interest to the two historians in Turkey was that it had been founded by a Trojan.
A lost work by Alcimus, perhaps written at the start of the Hellenistic period in Sicily, gives an alternate version of the Romulus and Remus story - where Romulus is the son of Aeneas; their daughter Alba had a son Rhomus who founded Rome (FHG 560 F - more on the sources of the Aeneid JSTOR and the various myths about the foundation of Rome here).
Recent excavations at Lavinium, traditionaly founded by Aeneas in honour of his wife Lavinia, have revealed that around the 'Mausoleum of Aeneas' (seventh century core with a fourth century superstructure) there were fourteen altars going back to the 6th century and a sanctuary of Athena Ilias lay to the east of it (the area is known as 'La Madonella'). One of the early altars honoured Castor and Pollux, the Dioscuri, twin brothers of Helen of Troy (ILLRP 1271a): Casstorei Podlouqueique quorois (To Castor and Pollux, the Dioscuri). An Archaic temple of Castor was found in the Forum. The Dioscuri had been the famous twins of Greek myth, whose story was told in many Classical sources. They were well known in Etruscan religion, for example honoured by a banquet in the frescoes of the Tomba del Letto Funebre at Tarquinia (below). There was something slightly magical about twins to the ancients, so when Livilla gave birth to twins they were called the 'New Dioscuri' in the inscription of the Julio-Claudian monument at Ephesos.
Although there are plenty of dedications from Tarquinia attesting the cult of the Dioscuri there, perhaps more interesting is another stele from Felsina in Bologna, Ducati no. 138, which shows the Dioscuri as twin riders (below, source). It was made in the same circle as the Felsina Stele above showing a wolf suckling a child.
These twin Dioscuri continued to be honoured by the Romans, but they seem the obvious influence on the Roman twins Romulus and Remus. Just as Diodorus of Sicily came to be called Siculus, so the man who founded Rome came to be called Romulus.
In most later sources Aeneas set off for Italy, and it is there that his descendants lived and eventually Romulus and Remus were born and the wolf suckled them. Romulus and Remus had long been the founders of Rome, but Aeneas only joined the story later. And once the Romans had conquered most of the known world, the victors could impose their version.