Inquiring minds want to know.
While Alan Lomax recorded a British folksong which mentioned jumping on someone’s bones, it was used in that case to indicated someone “stomping” on another.
The modern sex usage is first recorded in print in 1965, thusly in Esquire:
As an aside, the term boner to mean an errect penis only gets into print in 1966. Not trying to suggest any connection. Just interesting.
thanx!