Stopping co-ed sports by the age of ten takes care of any girls who start maturing earlier than average. A study by Youth Sports showed that boys and girls, prior to puberty, can compete against each other on the same teams, provided they have all had the same skill training. The physical differences in size and strength manifest themselves at about eleven years in females and thirteen years in males. The article also mentions that after these ages, males, in general, start getting taller, heavier, and show greater speed, strength, power, and overall size. Letting the kids' play with and against each other when they are going through the early stages of maturity is a bad idea.
Young boys start having different feelings towards young girls and vice versa.
The issue of competition is youth sports, is a tough subject, should it be more or less competitive. On one hand, you do want competition so that the little leaguers get the opportunity to experience the full effect of what it is like to be on a real team. On the other, the issue of having competition is a lot of pressure to be putting on a very young child. Being on a team for a child should be almost like a second family. A child wants to have the friendship, stability and trust that comes along with every family to be included on his team.