To be honest i do not know his age but he doesnt look thin or have the triangular look
How do u know what weight a bp should be btw?
There is no rule book that says your snake should be this weight and this length. They all grow at different rates. I have two snakes that are the same weight, one is 1500g, one is 1200g. The 1200g snake is significantly longer then the 1500g snake.
It just depends on the snake. 900g is a good weight for an adult male.