I like to think that the same Wonderbolts (at least, Soarin', Fleetfoot, and Spitfire) were around back when Rainbow was a filly (8-10 years). Since the original trio were probably young adults (18-20) then, that'd make them about 30 or 35 when Rainbow Dash is about 18 or 20 years old.

(this is why I don't ship SoarinDash because I feel like Soarin'/Rainbow would have a problem with the 10 year age gap between the 2)

EDIT: I remember the flashback with everyone as fillies including the future Wonderbolts, so uhhh... ignore this unless that gets retconned lol