How do i get fatter/thicker arms and legs?

I am fairly happy with my waist size but my arms and legs are EXTREMELY thin. I don't even know why, i eat a lot! So yeah, how can i get thicker arms and legs?
Some information:
13 years old
Female
5"5
17inch thighs
11inch calves
6inch arms

THANK YOU! =D
 
Back
Top