I started stuttering ever since I was like 7. So I've been going to speech therapy for years and during them I was told that people can just develop a stutter it doesn't really need a cause and when I did a presentation on stuttering I researched a bunch about it. That research lead me to figure out there are many ways to develop a stutter those being stress or some kinda traumatic event, physical trauma, or just being born with it. In conclusion I can't help ya with why you just suddenly developed it but it could be a variety of things. Oh also a stutter can randomly develop at any age.