If you can only acquire rats from a pet store I think it would be better to wait for him to be neutered. The problem with pet stores is that you can't see the breeding conditions the rats are coming from so you may be supporting bad breeding conditions or lineage. Many people have gotten rats or other pets from pet stores that have become sick or turned out to be a different gender then promised resulting in accidental pregnancies. If you don't have a nearby rattery, then what about a rescue? Meanwhile, you will want to spend as much time as possible with your male to keep him from becoming lonely.