It's uncommon but not unheard of. I knew someone who started stuttering at 20. Will it go away to stay forever? Who knows. What I'd recommend is not to focus on that. What I would care about is understanding that stuttering really is ok. It must be hard to go your whole life being fluent and having to adjust to something as confronting as stuttering, but take it from a lifelong stutterer, don't try to hide it. Don't try to be fluent. It is the source of most problems and only makes things worse. You're still you, both when your fluent and when you stutter. That's the key thing. And if it does magically go away, that's cool too.