I'm a bit of a jack-of-all-trades, master of none...
I started off singing in a cathedral choir, first as a chorister, then as a bass, until I was 17.
I learned piano and flute to Grade 8 from age 12-16 and then abruptly stopped getting any better at either of them.
I also took organ lessons for about a year (at age 15) and shakuhachi lessons with Yoshikazu Iwamoto at Uni when I was 18.
Then I became a self-taught terrible percussionist and timpanist ( great fun  )at university because there weren't many percussionists and I wasn't quite good enough to get into the orchestra as a flautist  . My finest hour as a percussionist was playing timps in the Firebird Suite in Durham Cathedral. It went great until near the very end when one of my sticks hit a kettle-drum tuning tap and smashed in half, sending the business end of the stick in a mighty 20-foot-high parabola and dumping it on top of the xylophone. I carried on valiantly, executing fortissimo rolls with one hand until the rest of the percussion team bravely passed a replacement stick along the line, which reached me just in time for the final sequence of very prominent timp strokes. I felt the warm glow of belonging in a team, something which I suspect is a rare feeling for a timpanist. 
I'm currently trying to improve my guitar-playing skills, but the only instrument I've really kept up is the piano, although I very, very rarely demonstrate this in public. 

You mean like,

Q: What do you need to make an orchestra?
A: 79 musicians and a timpanist.

 

I think you're right, Robert. It's a separate job, there being a Principal Timpani and a Principal Percussion. I often want to omit timpani from a score, and ideally replace them with percussion, but in most cases (even with quite simple percussion writing) this would involve the timpanist sitting the piece out and an extra percussionist being hired instead. Oh well.    (Once I wrote a piece without timpani for the BBC SSO and the timpanist said to me in the bar after a rehearsal "that's the best timp part you've ever written."  I agreed, and said that probably made it the best piece I'd ever written!)

My 'teamwork' experience was of course not in the professional arena: we all took turns to play the various percussion parts, so in he same concert I was playing bass drum in another piece and side drum in another.

Main instrument? Definitely the gramophone.

Attempts to learn the violin at the age of eleven came to nothing, because I couldn't make it sound the way I wanted it to immediately, but I play the piano after a self-taught fashion, and was the school timpanist during my last couple of years. As many here will be aware, I have on occasion been paid to sing, though not recently. 

For me, piano lessons from age 4-18 that abruptly stopped when I went to college (er, university).  I proceeded to perform there in fits and starts (things like the complete Ustvolskaya sonatas and chamber pieces by colleagues among the student composers), followed by a brief but highly enjoyable stint in an ensemble dedicated to graphic score realization in graduate school, but even that has tapered off essentially to zero.  Haven't had regular access to a piano now in more than five years, although I do harbor a serious hankering for a clavichord.

I very much wish I had experience on an orchestral instrument, particularly winds which (my recent compositional habits notwithstanding) are still fundamentally foreign to me on an instinctual level.

Started with the piano, still continuing at a serious level to the present day. Then came the violin, which continued until I left school in 2005. About the same time I started singing in a much-lamented treble. This provided me with the most unreplicable experiences of my life, in all sorts of professional circles. I still sing as a countertenor occasionally, though strangled cat predominates. At secondary school I was unwittingly subjected (poof! there was my name on the timetable) to taking up the organ, which continues as employment - but no more - to the present day.

[edit]For all this, neither of my parents have ever shown any creative inclinations. {re-inserted to make sense of KB's post below, but i do see it comes over a bit arrogant}

Trumpet and piano at secondary school. Was rubbish at both but tried, honest  Discovered I could sing a bit. The fact that I was a tenor helped. Sang lots: had lessons from a fantastic music teacher who in his spare time sang with Cappella Nova. Progressed through various choirs to some professional work. Crunch time came at 18 where I had to decide whether or not to keep on with the singing and apply to music college. 18 is not the best age for making such decisions  A burgeoning interest in wine, women and (non classical) song needs to be factored in here too. Ended up doing English and promising myself that I'd 'keep the singing up'. Now, the only singing I do is at parties, family gatherings, Christmas, etc. Oh well: c'est la vie. But to think that I used to be able to sing a high C... 

Thanks Martle!

Le temps des lilas et le temps des roses...