These are only as approximate, or at least as approximate as I can get them, I mean after all, no one can be sure of the 'exact' ages, after DB they get a little fuzzy.
Bra- 4 years at the end of Dragonball Z.
Bulma-16 when she first meets Goku in Dragonball.
Dende-5 when first appears in the Namek Saga.
Gohan- 4 (not 5 1/2 as is said in the dubbed version). 7 when future Trunks arrives. Age 11 he kills Cell. Age 16 he enters Orange Star High School.
Goten-1 year older than trunks.
Grandpa Gohan- 79 when he first finds Goku as a baby.
Goku- 5 at the beginning of Dragonball (he tells Bulma he is 14 but later at the first martial arts tournament he says he is only 12, he couldn't count before). He is about 23(ish) in DBZ, and 56(ish) in DBGT.
Kami- Over 900 when he fuses with Piccolo.
Krillen- 1 year older than Goku
Master Roshi- 123 (+?).
Pan- 5 at the end of DBZ, 14 in GT.
Yamcha + Tien- Both 4 years older than Goku.
Trunks-Chibi Trunks 2 when Bulma first introduces him. Future Trunks about 17 when he destroys Frieza and King Cold, 20 when he battles Cel (3 years later).
Chi Chi- 5 in the beginning of DB.
Vegeta- 30 something in the beginning of DBZ and 60 something in GT.