Im a 14 year old highschool frshman and i want to be a really good running back?

i am 5'9 172 lbs, and i want to play running back for my highschool team this football season, do you guys think i should lose or gain weight? Is 172 too big for a 5'9 14 year old freshman? and what should i do to build up great reggie bush type speed and great reggie bush type jukes?