How much do you have to stutter to have a stutter?

How much do you have to stutter to have a stutter? For the past few years I've sort of developed a stutter, I dont really know why, although I think it has something to do with my anxiety or lack of sleep, I also had a really bad speech impediment when I was kid so that might have a part in it. I don't think I have a full blown stutter, I only stutter like 3-10 times a day on average, but some days I stutter every sentence, and other times I don't stutter for weeks on end. So I guess what I'm asking is how much do you have to stutter for it to considered a stutter? And can you develop a stutter in your teenage years?