>>118035287It's a little all over the place. In the original pilot, it was an imagine spot of them 10 years in the future, so Dil was 10, Tommy was 11, Phil and Lil were almost 12, Chuckie WAS 12, and Angelica and Susie were 13.
Within the series itself, Tommy is said to be 10 at some point, Chuckie is 11, and Angelica is 12 up until the episode where she actually has her 13th birthday.