I'd aim for about 78* on the coolest side. Your snake is a young adult, so as already mentioned, this just may have more to do with that & not so much the temperatures, but do fix them anyway.
PLEASE make sure you regulate the temps. for safety as well as his appetite.
And I agree, if your snake is refusing food, I'd also lengthen the time between offerings, from a week to 2 weeks, & potentially even longer- because offering too often just stresses them anyway, & can make them LESS likely to eat.
Understand that with snakes, especially BPs- food refusals "happen", & remember they often fast in the wild, according to the seasons & their needs. As creatures that eat multiple times a day, it tends to worry us until we get used to the idea that snakes are just designed to fast at times. Sometimes it's just what they do.![]()