At the risk of asserting that it’s all folklore, this is, indeed, a bit of folklore that has been traditionally projected in modern times onto an unknowable aspect of prehistory. It’s also a sexist portrayal of the “earliest of times.”

This assertion about the role of prehistoric women depends on the idea that the first exchange of trade items was meat for sex. The mighty (male) hunter returns with meat, and the woman offers sex so she can get some meat. This idea is dependent on a crude understanding of what was likely going on in prehistoric cultures.

Hunters and gatherers were/are opportunistic food collectors. Anyone could hunt, and anyone could pick a berry or dig up a tuber. Many hunter-gatherer cultures have the men usually hunt while the women usually gather eatable plants. If there is an exchange for meat for anything, it would be for the plants, but even that idea of a prehistoric exchange depends on the idea that the men didn’t want to share the meat with women, and that the women had to find a way to leverage some meat away from the men.

That is an absurd portrayal of hunter-gatherer culture and is not likely what was normally going on in prehistory, although again, this is an unknowable aspect of prehistory and we can only speculate.

If there were an “oldest profession,” it should likely be credited to those who exchange materials or manufactured items. The presence of seashells in inland prehistoric sites or of stone for tools far removed from resource sites suggests that trade networks are a very old thing. These items were not likely exchanged for sex; more likely things were being exchanged for one another. This would make the trader (or the resource gatherer and the craftsman) the oldest professionals.