You're going to have people telling you that you're too young, but that's only indirectly the issue. The real issue is that at 22, most people are still maturing into the person they're going to be. At the very least, I think you should experience multiple, healthy, long-term relationships with different women. If, after those experiences, you never found yourself imagining being happy in the future of having children with any of them, that's a pretty good sign that kids just aren't something you're going to want. It's not so much age as experience, and at 22, you probably haven't had enough of it to be completely sure.
But there are a lot of people out there (male and female) who were felt 100% sure that they didn't want children by the time they were teenagers. Who are we to argue with that? The main thing to keep in mind here is that you should consider a vasectomy permanent. Although vasectomy reversal can often be done, about a third of the time it doesn't work. If you have any reason to think that you might want to have biological children in the future, then you owe it to yourself to do due diligence on this issue.
I had it done in my mid-30s after getting married. I had been ambivalent about having kids for a number of years and my wife didn't want any. It wasn't so much that I had it done for her. It was more that by committing to her, I had already imagined -- and was content with the idea of -- a future without them. And I felt very happy with that future. That cinched it for me. Don't let anyone tell you what you're sure of, but be honest and thorough when being sure for yourself.