Here are my answers (for whatever it's worth) to your 3 questions:
1. At the varsity level, coaches are expected to win. When a player reaches the varsity level, he should be able to compete successfully at that level. If he can't, he must either accept a smaller role on the team or run track! I know that sounds harsh, but eventually players must be weeded out ... that is the nature of the beast. And, personally, I don't like putting juniors or seniors on JV - that is supposed to be a "minor leagues" for your sophomores and/or freshmen.
2. In my coaching philosophy, I have 3 parts:
1- Every kid in my program should be a better MAN when he leaves my program than he was when he came in.
2- Success is possible only if you are willing to do what it takes.
3- Our program should be a family.
*I treat my players like my sons, and I never expect them to do things I myself haven't done or wouldn't do. My players are expected to carry themselves with class on and off the field (no cursing, grade checks weekly, sprinting on and off the field, etc.), and they MUST be a positive representative of their school, family, team, and community.
3. I agree that holding a kid back SIMPLY because of age or "time he has left" is wrong, but sometimes the coach knows more than anyone else in terms of how his "age" factors in. Sometimes, a kid is 15 going on 20 and sometimes he's 15 going on 13. I also like to think that I make these decisions in the best interest of the kid long-term, not in MY best interst short-term.
**I hope this helps. I'm a straight-shooter, so I hope you aren't offended by my comments.
Coach Knight