The year and month a child was born determines in what age bracket the child should play.  The US Youth Soccer & Alabama Youth Soccer Association soccer year is from August 1st of one year to July 31th of the following year.  Other sports have different "years."  Schools also use different "years" for placing children in a grade.  Very few clubs/associations have an Under-4 bracket.  Under-20 and older is considered "Adult Amateur" and not part of "youth" soccer.

Clubs that do not have enough players for single age bracket teams usually combine age brackets into U05/U06, U07/U08, U09/U10, U11/U12, U13/U14, U15/U16 & U17/U18/U19.  A team has to play in the age bracket of its oldest player.  So if a team consisted of 3 Under-5 players, 5 Under-6 players and 1 Under-7 player, the team would have to play in an Under-7 bracket.  Players can play "up" but may not play "down." 

A soccer seasonal year consist of two seasons, a fall season and a spring season.  Some clubs have teams only in one season but most have teams in both seasons. The spring season team is usually the same as the fall season team but occasionally some players may not be able to compete in the spring season.  In that case, there may be room to add a player or two after they are evaluated by the coach and the DOC.