It's pretty rare but not unheard of. I know someone who started stuttering at 18. The advice I would give you is not to try and hide or try to control/avoid your stuttering. Most of us have developed bad avoidance habits that are very difficult to get rid of. You don't do anything right to be fluent and you don't do anything wrong when you stutter. Treat it as another part of you that occasionally happens and know that even though it's probably a very weird and strange change, it's honestly not that weird and most people don't care if you stutter or not.