I'm 24 and I have a large bald spot on the top of my head. Is there anyway to grow back my hair? (photo)

Isolated Crown Baldness is a distressing pattern of hair loss. Generally the baldness keeps on increasing with age.If Hair Transplant is done early in life then there will be a progressive bald halo spot around the transplanted zone. Hair transplant can be planned only if the Hair is of thick calibre (preferably more than .08 microns), donor site has good density & area of hair loss is not progressive.

deprivation of nutrition and crash diets can be a cause of hair loss. However, looking at your picture suggests that you have genetic pattern hair loss. In your case hair transplant can be an option along with medical hair regiment routine to slow down future hair loss. 

You recent weight loss will have accelerated your genetic balding which is in your crown. From the photos you have vertex balding. You should meet with a doctor about it and see what could be done