I don't feel like citing sorces right now. :/
However, the Greeks encoraged an older member of the community (Erastes) to have intercural sex with younger members of the community, untill they were 18, then the younger members would become Erastes to a new "batch" of eromenos. Also, Sparta encoraged gay bounds in their army because it would keep the army strong, besides, men in Sparta did not get married until they were around thirty, and they lived in the barracks until they were around 60. (IIRC, I have to make sure of that exact age.)
But I should have said some, not most.