Playing ages are sometimes confusing and this is further compounded by recent changes in U.S. Youth Soccer regarding when each age group is defined. In the past, it was similar to school years (Aug 1st to Jul 31st) but now reflects the international standard (calendar years).
Each age group is listed as U (for under) and then the age (8) meaning U8 is for players under age 8. The ages are again determined by birth years (i.e., all players with 2009 birthdates are U8 players).
An easy to understand PDF reference can be found here to determine your player's playing age.
Bruce Samlan sets age divisions in our playing format by current registrations so when we have many players at the same age, this might be a singular division (i.e., U11 only) but often we combine two age groups together to field enough teams (at least 4) for playing (i.e., U7 and U8 will play in U8 division, U9 and U10 will play in U10 division, etc.) different competition each week. The combining of age groups in soccer is very common and permitted by U.S. Youth Soccer within 2 years which often creates the following age division breaks (U6, U8, U10, U12, or in other seasons U7, U9, U11, U13, etc.). In older divisions (over 14 years of age), playing age can exceed 2 years and more commonly reflects high school playing ages.