Age doesn’t matter but character compatibility does - two piggies have to like each other to be able to form a bond.
However, a younger piggy is often accepted by the resident piggy because a younger piggy cannot challenge for dominance. The benefit also is that if there is an age gap, then they will not be going through the big teenage hormone spikes at the same time.
Do you know exactly how old your piggy is? As he under 14 months of age ,then he is still a teenager himself.
The safest way to find a new friend for your piggy is by going to a rescue centre and adopting a new piggy rather than buying from a pet shop, if you have a rescue nearby. They can sometimes help ensure the two piggies have compatibility before you commit. If you buy a piggy and they do not get on, then its wise to keep a plan b in mind that they will need to live in separate but side by side cages.
If you do have to buy a piggy, then there are a few things to keep in mind and ensure you have prepared for a boar pair
You cannot quarantine the new piggy as they are likely under four months of age and piggies under that age need interaction immediately.
You must also check the sex of the new piggy yourself so you can be certain that you are getting a male to go with your existing male.
Space - two boars together need a large cage measuring 180x60cm (150x60cm as a minimum) as they are more territorial and lack of space can cause problems.
There is also the bonding procedure which you need to follow to introduce them to each other. You cannot just put the new piggy into Mocha’s cage as that will be seen as a territory invasion and cause a fight. The introduction must be on neutral territory.
The guides below explain more about the bonding procedure and boar pairs
Bonding and Interaction: Illustrated social behaviours and bonding dynamics
A Comprehensive Guide to Guinea Pig Boars
Boars: Teenage, Bullying, Fighting, Fall-outs And What Next?
Dominance Behaviours In Guinea Pigs
A Closer Look At Pairs (Boars - Sows - Mixed)
Journey through a Lifetime: The Ages of Guinea Pigs