Due to recent mandates by US Soccer, all soccer clubs in the US are switching to birth year to determine what age group a player plays in. For instance a player born in the year 2003 will play in the U18 age group for the 2020-21 season.
Also note that the format “U followed by age” really means that age and younger. For example, U8 should be read as 8 and younger.
There is another very important component to understand about this chart. To avoid players aging out of an age group during a season, the new top age group for youth competitions is U19. This change aligns with the birth year standard and makes sure that players are not eliminated from participating during the second half of a season. In short, all the existing U18 leagues should become U19 in the 2018-19 season and this change should cascade down the age groups (Ex: U17 becomes U18, U16 becomes U17, etc.).
2020-21 Soccer Age Chart