I joined Facebook in 2008 but don't recall if I used its messaging function at the time. I checked my old deactivated account and the oldest message is from 2009.
That's around 5 years ago now, so I'm wondering if Facebook deletes messages/inactive conversations older than 5 years? Being a teenager at the time I said some things I regret when messaging my friends over Facebook, so I'm certainly hoping this is the case.
Not that anyone would probably care enough to look, I'd just feel easier if there was no record of anything dumb I said.