I'm 14 years old and can relate to this alot. I've had no previous issues with talking, but suddenly I've started stumbling little and often with my words when recalling something or talking to my friends... I think it's mainly started due to stress and social anxiety. Also stuttering 2 or 3 times on the same word, and struggling to remember a certain word so I use a replacement one instead which usually just makes my point less valid... Maybe social anxiety could be something to look into :)