Anyone can be an athlete -- it's not how well you play but how hard you try! Make your sport a priority in your life - if you want to run... RUN regularly.. If you want to lift weights... LIFT them regularly..
The definition of an athlete does not have to do with the ability but with the amount of commitment to the task and reaching specific goals. Set yourself goals and push yourself to achieve them. Make sure they are Specific, Measurable, Achievable, Realistic and have a Time you want to have them done in. You will amaze yourself with how you improve over a short space of time. The body is an amazing thing in how well it adapts to what we want it to do!!
Having said that -- make sure you listen to your body. Respect it and it will treat you well. Give it the nutrition it requires for the sport you are doing. Rest it when it needs resting. Cross-train -- high impact sports such as running need low impact days such as bike riding to keep the fitness levels up but give the joints a break.
Being an athlete is also about how you define yourself. What makes a runner a runner or a footy player a footy player?? When they see themselves as that runner or that footy player and describe themselves as that!!