I'm 26, and the anxiety hasn't gone away completely, but it's a lot better than it was when I was younger. I think the more we allow ourselves to stutter, and just let it happen, the easier and easier it gets. I don't usually replay my stutters in my head as much as I used to when I was younger, which is progress for me. I think the other commenter is correct in saying that most people don't even care, and realizing that is really freeing. Knowing that the person we're talking to mostly won't be bothered by stuttering or even notice it sometimes is a great way to lessen the anxiety surrounding stuttering around new people.