Healthy weight for 3 1/2 year old ball python?

[dangernoodles]

Is it possible you could show some more pictures?
The sharp ridge sticking out on a BPs spine indicates it could be underweight.
He should be on small or medium rats right now (You are going to have to get him adapted to eating rats, you could scent a rat with a mouse.)
Its not exact, but a 3 year old male should be at least 800g.
Weights can vary.