Help Build My Running Back Body Type?

I am 14 years old and will be playing jv high school football next school year i am 5'3-5"4 and weigh about 118-120 and run a 4.8 forty and i want to know how and why i should build my body. knowing that when im done growing i wont be that tall i look to build my body after 1 of the three following nfl backs... Maurice Jones Drew short but stocky big thighs and arms /power back... Darren Sproles short but solid built body just small body frame straight ahead sprint type runner/ back... or Garrett Wolfe small frame and body strictly a back