Coach - speculation and second guessing *is* what happens at sites like this
I think it's hard to go with a set hard count to fit "all" pitchers because they are all different. Tim Wakefield could probably throw 100 every other day, but Roger Clemens could be one you'd restrict. Then again, wasn't it Bob Gibson that would always be well over 100 game after game. I think Nolan Ryan had quite a few high counts, too. There's a slew of old time pitchers that just threw and threw and threw. I guess that's the "old school" vs. "new school" argument.
I agree consistently >100 at this age will result in a lot of "second guessing". Going >100 in "a" game to get "a" win - that's on the coach to know what his limit and his pitcher's limit is. Obviously if you ask a 16-18 year old kid he's going to want to stay in. The testosterone is flowing and he thinks he's superman. My son's been in the 90's a lot lately (he threw against Salem in the BG game, coach). He's been throwing in the offseason and he takes care of his arm in between starts. He's one of those pitch to contact and stay around the plate. He may have gone >100 a few times, but I'm not concerned because I know where he's at and I trust the coach to make the right decisions.
As for the youth level I think it's up to the parents to speak to the coach. You don't get on a HS team or into college based on "a" LL/CR season nor do you get there from "an" AAU season. Coaches there may not be looking out for your child's well being. There's reasons why LL has enacted rules regarding pitch counts and catcher to pitcher swaps - there's too many coaches that cannot be trusted. Some AAU coaches are even worse - that's when you have know the goal of the program you got involved with. Did you go because they were winning all the time or did you go because you were getting better training. Unfortunately at tryouts you may given all the hot dogs and apple pie, but once you've paid your fee you get the brussle sprouts and lima beans...