With the way the age brackets are set up covering 3 years youíre always going to have teams at the upper end of the age bracket, teams at the bottom of the age bracket and teams somewhere in the middle.
The older teams are almost always going to have a physical competitive edge.
The guy who runs our league does an excellent job of ensuring each team has a good cross section of ages and sexes. For instance, my roster for this spring has 12 players (my only beef - WAY too many players for 5v5), with four each of 10, 11 and 12 y/o's.
IMO, the biggest thing leagues need to prevent is allowing team builders to keep a team together that dominates their division. Let them do it one year, and if they run away with it, you break the team up. Simple as that, I think. Restricting coaches to only being able to request 2-3 players would also help. A competitive league/division is best for EVERYONE involved. When you have a team consistenly winning by 15-20 points it isn't good for any of the players athletically speaking.