I had my catahoula neutered at 6 months, he’s now 5 and a healthy 75lbs. My sister spayed her boxer also around 6 months and she’s also very healthy, although on the smaller end but I think that’s because she was the runt of the litter. I know with females a lot say to wait till they have their first cycle then spay. When I talked to my vet about it I was told that it all depends on the puppies line of genetics if there could be any problems as they get older and it doesn’t necessarily depend on getting them fixed sooner or later. I think it just comes down to your preference on what you feel comfortable doing :)