I have heard of snakes shedding from every 6 weeks to only a few times a year so maybe hes just growing a little slower. Maybe someone else whos more experienced can help you, but Id say as long as hes eating and your not seeing any regurges, hes alright. Just be on the lookout cause eventually hell go into blue.
You say he flakes, is it the result of a previous poor shed? Maybe you could soak him in warm water and see if you can gently work some of it off......Ive never seen my snakes "flake" before