Well, I think you've got it the wrong way around. Put it like this: You don't stutter because you think of stutter - you think of stutter because you're in a situation involving stuttering. Also, when you don't stutter, you don't think of stuttering. But that doesn't mean that in order not to stutter, you have to not think about stuttering. In other words, it's not something that you're doing wrong. It's just that you have a stutter and it's something you go through. Btw. speech therapy is totally viable to pursue several times and continually. It's not something that age hinders.