Babysteps, you're on the right track. Everyone has posted good advice on training and proper diet. Get yourself a plan and stick to it. Pretty soon, you'll be bragging about how good you look in lycra. 14 is a tough age, as all those changes run you to the raggeded edge. The cycling community in general tends to be a supportive and forgiving group of folks that encouages everyone to just turn some cranks. Talk to your bike shop owner/manager/head gruru about rides, clinics, and even races in your area. Nothing boosts self esteem like a shelf full of trophies. Set some goals, just not big ones.
That almost sounded like a comencment speech from Chris Carmicheal.