Upright bass: Began at age 8, played for one year, moved to cello.
Cello: Began at age 9, played for five years, gave it up, recently picked it back up.
Bass guitar: Began at age 14, played more or less ever since, though when I was in bands I'd more often play guitar. This is a record on which I played bass. P Bass, then terrible Ibanez, then another two P Basses, so basically P Bass all day, though I'd like to try out one of those Harmony H22 reissues.
Guitar guitar: Began at age... 17? I don't know. I don't even know how I ended up getting a guitar but I did, first a Jackson V then an Epiphone SG and Les Paul. The Les Paul I still play, it's white with gold hardware and a black pickguard - it looks better than it sounds (in my hands) but useful for recording. The SG is just a practice device for idle moments. I've also got a Seagull acoustic that lives at a friends' place, currently. I was in more bands as a guitarist but I was always the weak link. Speaking of links, I'm not sure if this one works.
Software: Probably age 12 and on. This is the only constant, as even when I was in and out of bands I'd screw around with home recording, softsynths, sequencing, sampling, programming. I'm not very good at it but I do it.