The youngest Bitcoiner I know of is
nahtnam. He should be around 15 years old, seeing that he stated that he was 13 over
here (which was two years ago). The youngest Bitcoiner I personally know is 17 and I'm 20 years old myself (will be 21 next week).
Damn, 13-15 is young, though I guess kids are getting more tech aware and involved these days which is a good thing. I hope getting involved in bitcoin so early will pay off for them in the future. They might be able to take early retirement if they save well.