Ancient jews interpreted just about everything allegorically, but literally also. I've not read anything from Josephus indicating he didn't believe Adam was a literal person. In fact, I don't know of any fathers that didn't believe in a literal Adam. They attached allegory to just about everything, but not as a substitute for the literal.
The key is in understanding the terms. Allegory to them was what we often call typology. The early fathers attached futuristic predictions to literal things like the days of creation, but still believed in the literal days. That's why they virtually all believed the world would only last for 6,000 years, because they believed the literal days were also types for 1000 year future periods. They were six literal day young earth creationists, but allegorists regarding the future. Ancient allegory did not negate literal interpretations. Ross and others have missed this important distinction. And even the few that weren't 6 day literalists, still believed in a young earth and fought the old earth philosophies of their day. Despite pressure for their culture, they fought for a young world.
Antiq. 1:34 (1.1.2) Moreover, Moses, after the seventh day was over,1 begins to talk philosophically; and concerning the formation of man, says thus: That God took dust from the ground, and formed man, and inserted in him a spirit and a soul.2 This man was called Adam, which in the Hebrew tongue signifies one that is red, because he was formed out of red earth, compounded together; for of that kind is virgin and true earth. 35 (1.1.2) God also presented the living creatures, when he had made them, according to their kinds, both male and female, to Adam, who gave them those names by which they are still called. But when he saw that Adam had no female companion, no society, for there was no such created, and that he wondered at the other animals which were male and female, he laid him asleep, and took away one of his ribs, and out of it formed the woman; 36 (1.1.2) whereupon Adam knew her when she was brought to him, and acknowledged that she was made out of himself. Now a woman is called in the Hebrew tongue Issa; but the name of this woman was Eve, which signifies the mother of all living.
Antiq. 1:37 (1.1.3) Moses says further, that God planted a paradise in the east, flourishing with all sorts of trees; and that among them was the tree of life, and another of knowledge, whereby was to be known what was good and evil; 38 (1.1.3) and that when he brought Adam and his wife into this garden, he commanded them to take care of the plants. Now the garden was watered by one river,3 which ran round about the whole earth, and was parted into four parts. And Phison, which denotes a multitude, running into India, makes its exit into the sea, and is by the Greeks called Ganges. 39 (1.1.3) Euphrates also, as well as Tigris, goes down into the Red Sea.4 Now the name Euphrates, or Phrath, denotes either a dispersion, or a flower: by Tigris, or Diglath, is signified what is swift, with narrowness; and Geon runs through Egypt, and denotes what arises from the east, which the Greeks call Nile.
As you go down the story, all individuals were literal. Cain literally murdered Able, built a literal city etc. And a lot is added to the Biblical version, so it was not his only source.
Here's a good article on Josephus.
Josephus says, ‘Genesis means what it says!’