Frequency/amount fed to 5 month old corn

I got a corn snake about 3 weeks ago, and have been feeding him a pinkie every 6 days, as seems to be recommended. His feeding logs from the pet store however, have him eating 2 pinkies about every 7 days (it occasionally was 6 or 8 days). Should I bring him to 2 pinkies? If so, should it be every 6 or 7 days, and how long should I wait between mice? He seems to be doing fine currently, but if he's not getting enough to grow well or something, that wouldn't be good.

For a start, you will need a gram scale to weigh your snake and the prey. We usually calculate the prey amount and span by weight of the snake and prey.
Some snakes are bigger and some smaller at the same age, so it's difficult to tell without you weighing him.

It seems to weigh about 15 grams.

15 gr is the point the Munson plan recommends switch to 2 pinkies. Munson plan is very aggressive, though. You can wait until he is 18 gr, and make it 2 pinkies every 6-7 days from then on. For now you can yet stick to 1 pink every 5-6 days for some feedings.

I appreciate your concern I'm still a nervous wreck 're food size and amount!!!!! I have followed the Munson plan to a certain extent ie waited a month after that recommendation just to be on safe side as already said I was also told it is quite aggressive so I am following it with slight delay !!! After experiencing regurge I am very cautious .We have just moved up to one small fuzzy and Theo was 32g so technically should be on medium fuzzy but we are getting there slowly .Good luck x