I definitely feel kids these days spend much less time being kids.
I have daughters, and when I go to their school school I see more girls trying to look and act like women than I ever remember when I was that age.
When I was a teen there were a handful that had lost their virginity, had blossomed quite young and were able to get in clubs etc - but that was the exception more than the rule.
These days half my 14 year olds class would easily get into a bar without question.
Problem is, despite looking the part they arent any more mature, and I cant help feeling that rush to grow up can be quite damaging.
That said, 70's and before was renowned for older guys/younger girls and attitudes to it then were pretty relaxed. I think it was through the 80's/90's attitudes changed more. Chances are that sort of activity just went behind the scenes more as you say. I suspect it didnt just stop.