If you are just asking about the sports, yes, it will make it harder for a boy to compete against older boys for a place on a school team based upon years of play and physical development (which might not matter in your son's case as you say he is a year older anyway). As someone else pointed out, it does not matter for outside of school competitive sports which are based on age, but school teams are based on grade level. If he is accelerated and has a hard time making school teams with older boys, you might be able to look at age-based sports outside of school, e.g., AAU basketball.
http://www.aauboysbasketball.org/RulesInfo/AgeCalculator.aspx
