Are you sure that you weren't used to stutter during early age? For me, I might picked stutter when I was 3 or 4. I had mild stutter till 7-8. After that my stutter vanished (not completely, almost nil, I guess, I would still stutter, but very (very) rarely (mosty on "K" words), then I again started stuttering mildly when I joined a new school, at that time mine age was 16. I was a shy and introvert kid (I still am), so it was a big deal for me to join new school and make friends. Not to mention, anxiety filled introductions to every staff member and classmate. Now I'm 21, in second year of engg. and can't even pronounce my name. I guess, I shouldn't have joined school that time. Lol. So, my point is stuttering can vanish and can come back, in most cases, due to certain incidents causing anxiety, which you've never experienced before.