I agree, looks like a good size for him. If you have a digital gram scale, you can weigh your snake and track his growth.
To determine the right size of mouse by weight, most people use the Munson plan:
-When they're on single pinks (2-3g), feed every 4-5 days. (Snake = 4-15g)
-Double pinks (3g x 2) every 4-5 days. (Snake = 16-23g)
-Small fuzzies (5-7g) every 5-6 days. (Snake = 24-30g)
-Regular fuzzies (7-9g) every 5-6 days (Snake = 30-50g)
-Hoppers (9-12g) every 5-6 days (Snake = 51-90g)
-Weaned (14-20g) every 7 days (Snake = 91-170g)
-Adult (24-30g) every 7-x days (Snake = 170+)
-Jumbo Adults (40-50g) every 7-x days (Snake = 400g+)
It's a somewhat aggressive feeding schedule, so I usually wait until the snake is well into the weight range before moving up sizes.