Tee Ball is for beginning players, league ages 5 and 6 (some 7) typically Kindergarten or last year of pre-school.
"A" is for players league ages 7 and 8 (some 6) typically 1st and 2nd grade.
"AA" is designed for primarily for players league age 9 - 3rd grade - but also 8 year olds who have successfully demonstrated "A-level" skills, as determined by their coach, and are ready to begin pitching and hitting live pitching.
"AAA" is generally for players league ages 10 and 11, who have played at least one year at the "AA" level
"Majors" is for players league ages 11 and 12, with a limited number of 10 year old players.
"Juniors" is generally for players league ages 13 and 14.
"Seniors" is generally for players league ages 15 and 16.