The short answer is no you can't tell age from size. First is he absolutely a male? here is my example I have a pair of snakes born the same time and they are now just over a year old one is 880gm and the other is 1690gm they have been fed on the same schedule and correctly sized meals they rarely refuse food and are kept under the same conditions yet one is almost twice the size of the other. I have a disadvantaged female that was born 2 months earlier and is only 400 gm and she never refused food she was born small and has stayed that way. I am 220 lbs and 6'4" how old am I? We are all different so are snakes no two are the same.