Laura
i got my belt when i was 15 and the rest on my 16th birthday. to be honest, it was already too late, i think if you start slowly at 14 (by the hour, at home, later at night) it's better.
with 15 after one year of training you can wear your belt permanently so you had enough time to get used to it.
the reason is my own experience, i started mastubating when i was 14, it's easier to prevent this early than if you've been around longer.
also few girls with 13/14 already had sex