Well, okay, it's more of a "guesstimate". Since the show hasn't stated it explicitly, I've been trying to suss out when exactly the Queen's Gambit sank. There's some extraneous / redundant information in here just to illustrate my thought process.
In the pilot, the TV news reporter says that Oliver was found "more than five years" after the Gambit sank. Assuming that Starling City time roughly corresponds to our real world time, that means it was autumn 2012, so the shipwreck happened in 2007 but earlier in the year.
Oliver and Tommy were born in 1985, according to their respective headstones. Oliver's birthday is May 16th. Tommy's is sometime in late February (again, assuming SC time roughly correlates to episode air dates).
Laurel was in the same class in school with the boys since at least eighth grade, so she's roughly the same age as them.
That would make the trio about 21/22 years old in 2007, and Sara 19 or 20 (born in 1987).
Sara was unexpectedly home from college for "a three day weekend", so it was probably not close to her scheduled spring break, which tend to happen in March.
Moira assumed Oliver had classes to attend ("Not so much.") when the Gambit left port.
Laurel was close to the end of her undergrad program. She had "just applied to law school", which one usually does in the autumn of senior year.
tl;dr -- I'm a giant nerd who thinks way too much about the timelines of fictional worlds, but I'm pretty sure the Queen's Gambit sank in late winter / early spring of 2007. Maybe in February? (Man, would that have ruined Tommy's birthday. Now I'm sad. I'm so sorry, you guys.)
