Juniors have been able to bowl in open events as well as leagues/tournaments since the game started [unless specific rules precluded them and such rules are probably now not applicable in this age of political correctness].....
It may have been different in each state/territory, I'm not sure.
I do know that no junior was allowed to participate in an adult (IE: money) league down here until 1990.
That is, if they wanted to keep their junior status in order to participate in things such as President's Shield etc.
There had been a fair few of us in the junior ranks that had wanted to bowl in the adult leagues back then (for stronger competition - and to show off in front of the bigger crowds let's face it
) but were precluded from doing so.
I asked to join Sponsors League at Moonah, at the time the biggest and best standard league in the state, at age 12.
The request was denied and because I wanted bowl President's Shield in future years, decided it was wiser to stay in the junior leagues instead until the rule was changed when I was 15.
The old STTBA were a very strict organisation in those days and rocking the boat wasn't a very smart idea.
I can definitely say it was the best thing ever when they allowed us to join the adult leagues and bowl against the men, it was like a whole new world had opened up.
As for tournament play, back in that era it was strictly forbidden for any junior to play in any adult tournament and even when the 1990 ruling was brought in, we were still barred from entering adult events until we turned 18.
Hence why many of the Junior/Adult classified events they held at Moonah pre-1990 were very strongly participated in back then - I can remember one had over 90 teams participate!
As to what Androoo said, I agree 100%.