I'll second what Spence said about joining a sports team or club, I’m 15 too and am dead set and motivated to join the Marines I've been training since I was 13, but it's still 3 (ish) years away so to get up early mornings and training/ training when you really feel like you can't be bothered is hard . Having a goal such as a up and coming fight/race/match etc give you that extra motivation.
Just get out there and do it really, weather its sports, running for leisure, circuit training, lifting weights etc it all helps.
As well as training for what ever goal it is you are training for be it the RM or sports be sure to also live a healthy and active lift style (yes I do know how cheesy that sounds

) but eating health, drinking plenty of water, walking some where instead of getting a lift etc all adds up.
Just on a personal and very bias note, if you live near a boxing club get your self down there, since I started boxing my fitness went sky rocketing but it is also good laugh as well as bloody hard work.
Welcome to the forums by the way
Stokey
P.S. Feel free to Pm me if you like, being the same age similar goals might be worth having a chat .
All the best
P.S.S. just seen euro_andrew's post and agree with it in most parts especially .
get some combat boots to walk in and get yourself some nice blisters now, so you don’t get them in training.
I've been doing some tough walking with a mate of mine for a little while now, attempting and sadly failing a tough 150 mile walk last summer the blisters I got where god awful but I found out how to treat them etc plus my feet toughened up no end.
Just don't go running in them or anything like that... if you really want a challenge try (maybe with a mate) walking in the lakes (or somewhere like that) with a Bergen. maybe a few days walking camping along the way.
those types of trips are great, have a smashing laugh, improve map reading and confidence, wear out your legs and get you used to walking with boots and a Bergen. All that hard work in the day getting from A to B is worth it when you sit down to cook your self some super noodles and a brew
