I started piano lessons when I was five, so I suppose that particular decision was based on the fact that my mother and sister both played.I remember seeing James Galway on a children's program when I was little and being fascinated by the flute. I started on that one as soon as they let us start learning instruments in school, which was fourth grade. In fact, I still have that flute [named Syrinx], although I need to replace a pad on one of his trill keys. Slipped it two days before a jazz concert this spring [*%&*#!]. When it's in the budget, I intend to pick up wooden flute as well because I like the warmer tone.
When I started high school, I decided to take up saxophone to join the jazz ensemble. Never actually managed to join the jazz ensemble, couldn't spare the time commitment. But I marched alto for a year and then switched to tenor. I'm not sure why I chose that particular instrument, except that I've always liked the smoky tone, and the hybrid nature of the instrument intrigues me. Last summer I got myself a Conn tenor and named him Duncan.
My fall project is to get back into piano lessons, since it's been about six years since I had a formal lesson, as a music minor I can take instrumental lessons free of charge, and I have an opportunity to study jazz piano. Some day I also mean to learn guitar. Again, though, that must wait on my humble student budget. :)