My 14 year old types faster than most adults. And has been able to do so for a couple of years. She wanted the skill for the game One Hour, One Life and there are free typing apps out there.
I was about 9 or 10 years old when this moment happened mind you, I was typing with two fingers, one on each hand, nowadays I use at least three or four fingers per hand to type, which is a lot faster.
When I was 9, we had a typing class at school and I learned to touch type (i.e., 10 fingers) at about 20 wpm. By 12 I was up to 40 or more. I suppose I would have been blocked.