At what age should I get my boy piggy neutered?

I've never had a male piggy neutered but from what I have heard it's probably best to wait until your pig is at least 3-5 months old so he will be fully 'developed' - make sure you ask for advice from your vet - and able to cope with an anaesthetic. Make sure you have a good reason for getting him neutered as it is surgery and requires an anaesthetic which can be very risky. If you're getting him neutered just so he can live with your female piggy, maybe just put a separator in a large pen so they can live in the same pen and be company for each other, but can't actually 'get' to each other.

it depends on the situation. If you have to put him in with females, you need to neuter him before doing that, and give him about a month for everything to get out of his system. If possible, keep him in a separate cage until he's 3-5 months, but he becomes sexually active as early as four weeks old. That's why male bubs have to be removed from the nest at four weeks, or they can impregnate their mother and sisters.
It's always better not to have any major surgery performed on piggies unless it's really necessary. Piggy's breathing slows down radically under anesthesia, and if kept under anesthesia too long, they become hypothermic and die. That's why it's so important to get a good cavy vet, as any surgery is dangerous, and bad surgery is the worst.

Yeah, that is true weird but true they can enpregnante their mommy if they are not taking away from her in 3-4 weeks of age. I personally would not neuture my boys I have read a lot of horrible things about neuturing cavies.