A shop that dumps an stressed unneutered male and a female guinea pig together in a tiny cage that is already the territory of one of the piggies and then are surprised if there is an aggessive reaction? How much do you think they know about guinea pigs?
Boars can live together and can be bonded at any age. I even know of a 6 year old single boar in Australia who has found great happiness in his old age with a younger rescue boar in Australia! My own boar pair has a two year age difference.
However, there are some considerations you need to make:
- cage sizes: Guinea pigs are ground roamers that need much more space than you might expect. Cages that are too small are one of the biggest reasons why guinea pigs fight because they cannot get away from each other as they would normally do. This is especially crucial for hormonal teenage boars. However, I doubt that cage sizes in Japan go beyond what we would call a "small hamster cage" and I also know that flats are often very small, so space is cramped.
Cage Size Guide
Boars: A guide to successful companionship.
Boars: Bullying, Fighting, Fall-outs And What Next?
- as much as piggies need company, they are very much like people: they have likes and dislikes and do not necessarily get on. The key to any successful guinea pig bond is mutual liking and character compatibility, not age or being related/litter mates.
Unfortunately, I don't think that you have the option in your country to let your little boy choose his friend at a good rescue unless you look for no longer wanted boars that you and your boy can visit to see whether they get on before you bring one home in order to minimise the risk of ending up with two guinea pigs that do not like each other. However, you run a high risk of ending up with medical bills in case the new guinea pig is neglected and traumatised. it requires experience to bring these guinea pigs out. I have a room full of happily bonded second-hand guinea pigs, but I am lucky to have access to many guinea pig rescues.
Your other realistic option is to get hold of another guinea pig and keep them in next door cages if a same sex bond is not working out. If you have a sow in the next cage, they cannot ever meet unless one of them is de-sexed (or you end up with lots of babies - and a rather high 1:5 risk of a pregnancy going wrong!), but they can still keep each other company through the bars. You need access to a vet that is experienced with small furries/exotics operations for a boar neutering operation to not have a high risk of complications or even fatalities.
Illustrated Bonding / Dominance Behaviours And Dynamics
Guinea Pig Facts - A Short Overview