Honestly, Smuggler always struck me as the oldest one of the bunch. Not by much, of course, let's say if other characters are around 20-21, Smuggler would be 27-28 like Han Solo in Ep IV.
Smuggler's overall demeanor (based on their dialogue options, regardless of DS/LS inclinations) creates the impression of somewhat experienced person who's already seen their share of galactic stuff prior to the beginning of their main story, whereas Trooper/Agent/Knight/Consular are fresh out of training, SI was former slave and SW begins as merely a talented acolyte. Can't recall anything about the Hunter though..