Hi!
That is a great idea, especially if you plan to date him at a rescue for a wife or two of his choice, so you know that they get on when you bring them home. No piggy should be condemned to a single life just because pets@home sell baby boars in often too small that are not personality matched and then fight and fall out when they reach the teenage hormones. In the English speaking world, it is preferred to wait until the testicles have descended at 4-6 months of age.
With dating at a rescue, you can make sure that any new companions are quarantined and healthy, guaranteed not pregnant (any incoming sows undergo a mandatory 10 weeks pregnancy watch) and that the piggies decide whether they gel or not, so you do not need to worry about the bonding. You can look at sows of any age.
Mutual liking is the decider. But it helps you neatly avoid all the usual pitfalls tha can await the unwary and is worth going that bit further afield any time for utter peace of mind, so you come home only with a companion/companions were acceptance has happened and you have the support of a rescue in case things go wrong.
Important is finding either a general vet with plenty of practice in boar neutering (usually for a guinea pig rescue) or an exotics vet with experience in small furries ops. Rescues may be able to help woith recommendations on that score, too, especially if you are a future adopter. This helps to cut down on the risk of post-neutering complications.
Secondly, you need to factor in a 6 weeks post-op wait. Tegan, the little baby in my avatar on the left is the unplanned daughter of a supposedly safe over 5 weeks-post op boar (not one of mine!) It can really happen as late as that. This is why all good standard rescues now practise a 6 weeks post-op wait. Even despite quite a large number of rescue boars being neutered these days, I have not heard of an accident after this time - and it would make the rounds in rescue circles like wildfire!
If you are worried about neutering, some rescues offer boar-boar dating at the rescue under expert supervision. You can basically bond boars of all ages, provided they are character compatible. Dominant teenage boars are usually the most difficult to bond and can tax any new bond once their baby companion is hitting that time, too. But boars tend to mellow as they get older and the testosterone output is no longer so high.
Guinea Pig Vet Locator
Guinea Pig Rescue Centre Locator
Tips For Post-operative Care
Guinea pig castration explained (be warned, it is graphic!)
Here is a video of my Nye on the evening after his successful neutering op in January. Her has made a perfect recover and has had no problems whatsoever. His neighbour is a spayed sow by the way.
I'm going to neuter him asap then go for the dates after the 6 weeks? X