If I could go back to being a kid, I'd do what I've just started doing now: learn Violin and Piano. When I went to secondary school (about 12 years old) I was given a Cornet to learn by the music teacher. I can't remember if I chose that instrument or he just decided, but that's what I started with. I did enjoy it, got to 1st Cornet in the school band and loved that (the whole sense of being a part of something big and part of creating such a big sound). At about 14 I started learning to play the drums.
I'm in my early 30's now, I've been in rock/pop bands for over 10 years, but also wishing I was still in a big band of some description, or more precisely an orchestra. It took me a long time to realise how much I miss all of that. So I'm doing something about it now, just because I love playing music, and also I hope I can at least get involved in some amateur orchestra at some point.
I'm absolutely kicking myself I didn't do it earlier. Violin especially is starting to become an addiction already, I can't wait to get home and practise each evening - I try and do at least 2 hours per day.
I'm Hoping I've not left it too late to at least get fairly good with it, and hoping my previous musical knowledge will help a bit too.
PS this is my first post on this forum