I don't know about Ginsberg, but I do know that the ACLU filed a "Friend of the Court" brief on a Kansas case involving a mentally-challenged 14 year old boy and the 19 year old man that was caught having sex with him. The brief included the position that consent to sex should begin at age 12 for both sexes, and that the man raping the boy should therefore not be guilty of a crime.
I'd love to post a link, but the only one I had was on CU before the old stuff was lost...and my last search turned up nothing online.