I was born in 1969, played my first high school gigs in '83 (14) and first bar gigs and local festivals in '84 (15). I was probably a bit younger than most of the people around, but there were a lot of high school aged dudes playing out at that point. Drinking age was 18 still, and nobody cared if you were underage - no penalties against the bar as I recall, and I think we were actually legal on stage at 16. I'd just help haul gear in from the ally and then just stay there for the evening. No problem. No big deal. (I was tall too, so that definitely helped.)
Anyhow, lots of guys by 16/17 locally, mixed in with lots of 20-somethings. It wasn't segregated by age.