Yeah I agree, when I did my first sprint I was certain I was well prepared.. all except for whole the running off the bike thing. I ended up walking about 10 times (although the run course was ridiculously hilly) but you get used to it.
At 16 its great that your into the sport, I'd just suggest giving it a go and see how you like it, enjoy racing then as you do a race, or two, or three you'll start to see areas that you can improve on.
If you find you enjoy it then find your local club and join up. Clubs in the UK seem to be really well organised and tend to have a good few training sessions (usually coached) every week. You'll get plenty of advice and help from any good club at these sessions.