I bought my first, a 72 or 73 Honda TL125 trials bike, when I was about 13. Actually, I had no idea what 'trials' meant, at the time. I rode it for a couple of months on our farm. Really enjoyed it - until something went wrong.
I had someone look at it and tell me the crank needed replacing and was going to cost about $300 (roughly what I paid for it). I unloaded it, instead.
A few months later, my older brother and I went in together on a Suzuki RM100, which I rode the crap out of for years, until I was 17ish.