I've never officially had training, but I used to read a lot of material and practice on my own when I was younger. It probably doesn't account for much, but it was still fun, especially training with a quarter staff (like Donatello). In my teens, a bunch of friends and myself starting a mini-fighting league and it was a lot of fun.
I'd like to get into martial arts officially, but I'm going to wait until I get in better shape before I do so. I've had friends who've taken Aikido and Judo, and they've had good experiences being MA newbies, so hopefully that's a general ideal. Just don't get this asshole to train you: