You will still have trapped kids at U13 and U19. Think of all the parents who hold their kids back a year because they have a late June/July birthday. Around here they do it so they'll be bigger for football when they get to school ball. But that's still going to put them playing soccer with the wrong grade of kids. And the clubs all want to say not to play up because there is a difference, especially early on (u13/u14), with lots of kids and growing at different stages. I was never a fan of the school year age groups and my son was part of the 1st group for birth year. His best friend, 32 days older, was moved to the 2005 age group while my son was a 2006. At least with birth year there is no doubt which age group you belong to.