Hi,
it's actually an easy question. I have a 2.5 year old ball python.
He is a male and about 42 inches long. His head is rather small (about 1 inch long and 0,6 inches wide).
Now recently when I saw him laying stretched out he appeared a bit skinny to me. You can definitely see his spine but when I took a closer look at him he seemed fine. He only looks skinny from afar, not when you look at him closely. His girth should be around 2,2 or 2,3 inches.
When I got him (the breeder told me he was eating small mice weekly when he was 4 months old; he was around 100g when i received him) he was rather small.
Could he just be a naturally skinnier ball python?
(I also tried to take a photo of him stretched out but he curled up every time I tried to do that, so I eventually gave up. However I will attach two other images (hopefully they are somewhat helpful).)