Sadly, many establishment owners don't want under-age players even when it's legal in their local. "They just cause trouble", I hear, or "They tear up the tables!" I think these folks are missing the boat. You can have junior leagues and tournaments with a supervisor and strict rules of conduct. Years ago, I played in a pool hall in Iowa that did very well by running junior leagues. The owner was smart enough to realize that he could create his own customers, before they came of age and chose to play in bars or other pool halls. When I was in high school in Wisconsin, almost every high school had a bowling league and it helped make bowling huge in the '50s (along with tv coverage of the pros).
So I blame proprietors for the absence of young players. When their businesses go down, it's usually their own fault for not promoting the game properly.
Donny L
BCA/ACS Instructor
Gainesville, Fl