I think your vet is mistaken too, keep feeding every 5-7 days while he's young, & transition to longer intervals when he's eating larger prey items.
Exactly what are you feeding him now? A young BP of his or her size is big enough to eat small mouse hoppers (preferably f/t- that's "frozen-thawed"), which would NOT be digested every other day. The only thing your snake might digest that quickly would be mouse or rat pinkies (hairless, eyes closed) BUT neither of those would be enough food, nor a proper meal for a hatchling BP.
Also, a 17" BP is not too small to determine the gender; it sounds to me like your vet is just unfamiliar with snakes & doesn't want to say that.
To find a more experienced herp vet, this site might help, & you might check to see if the vet you just saw is listed there too- I'm betting "not".
https://arav.site-ym.com/search/custom.asp?id=3661
By the way:
A quick afterthought: don't be in a rush to determine the snake's gender- vet visits tend to be stressful for the snake, & it's FAR more important that yours is eating well & growing now. I wouldn't take him or her to ANY vet unless something seems wrong that general husbandry (care) won't fix. That's what we do here- help you sort out issues so snakes don't become sick in the first place. Honestly, unless you have a real reason to determine the gender (breeding), it's not even important.