14, listen to me man. Chill out, you still are going to grow. You stop growing until you're 21.
Not going to bully you, but if motivation is what you want then that is what you're going to get with a little of "TOUGH LOVE"
Listen here fat boy! Put down the Cheetohs and eat an apple. And that show you wanted to watch, guess what? GOT CANCELED. Now get up and move. Get on that bike you haven't used in like forever. And when you get back home, don't you dare look at that soda. Get a glass of water. No wait, make that 2 glasses of water. Chug them down. Now shower time. When you get out look into the mirror and ask yourself. Did you give 100%? Can i do this tomorrow? For the rest of my life?
REPEAT UNTIL YOU ANSWER YES TO ALL THE QUESTION. You are now motivated.
Lol, to be honest I don't think any young person still growing into their body should do exercise. It is understood that now a days our young children are growing up with an obesity epidemic at an alarming rate. But who can blame them, with technology advancing so quick has a grasp on their entertainment. Kids needs the latest and greatest thing out, it gives them that cool factor with their fellow friends.
But what would be nice is kids being active and eating healthy. 2 things that kids more than likely will not do if its hard or difficult to achieve.