Since the search feature on this site is so appealing, I'd like to say that my dad suddenly developed a stutter when he was an elementary student. In his case, it was because of psychological trauma within his safety-zone. Without going into details, he was pulled from a loving environment into one not-so-loving.
He withdrew and began stuttering for the first time. He found his equilibrium once again (as a teen) with the help of some healthy doses of a hobby he loved that gave him an escape from his environment, and the stutter went away.
I bring this up because stuttering can crop up at a later age, and may be from a "triggering event (mechanism)" as Dude noted.
