Some people feed once a week with no problems, but I too feed my younger/growing ones every 5 days. I believe his problem was the size of the feeder that contributed to his slow growth: hatchling BPs can take small mice from the get go (mice fuzzies are too tiny) so I think small mice are way too small even if he's a smaller guy. I would get him on larger mice or at least rat pups and go from there.
When you get your scale I do the 10-15% rule: feed a feeder that is that percentage of your BP's weight.