I did music GCSE for two weeks, and then decided to wander over and do a Drama GCSE instead.
I played keyboard back then, to a pretty low standard. Now, I play bass, again to a pretty low standard. I've barely touched it in recent months, and half the stuff I knew i've forgotten. I'm all self-taught though, I only got it as something to mess around with, not something to do as a serious hobby.