I'm sorry for your loss.
Age is not relevant. Its character compatibility which is the determining factor of a successful bond. If possible look to rescue centres who offer boar dating so he can choose his own new friend (regardless of age). However, given the current lockdown situation, it may be harder so getting yourself on a waiting list for dating for when it is possible again with restrictions lifted is a good idea. As he is right in the middle of his teens with hormones flying, bonding with another boar can be trickier, not impossible though, so having the help of a rescue centre in finding a good match is a good idea. If you buy a piggy on spec from a pet shop for example, then you will need a plan B in mind in case the bonding doesn't work and they dont like each other. In that event, they would need to live in separate but side by side cages for interaction through the bars.