I don't think that was a snake that I produced,was it? You didn't contact me recently so I assume it wasn't one of my babies unless it was a secondary sale.
I would say that if it is eating and has survived almost a year, that there is nothing wrong with it. A lot of snakes don't eat in the winter even if it is their first winter and kept warm. Babies from a litter all grow at different rates and bigger and fatter is not necessarily healthier. Some snakes are picky feeders their whole lives. Some of my pickiest eaters are good breeders and some of my chow hogs are not. He may end up being your best breeder and live a long fruitful, healthy life. I would not be concerned, as long as he isn't super skinny, which he didn't look in the picture.