16. We use when, not as or while, to talk about ages and periods of life.
When I was 14 I first got interested in archeology. (NOT As/While I was 14...)
We lived in London when I was a child. (NOT ... ̶a̶s̶ ̶/̶ ̶w̶h̶i̶l̶e̶ I was a child.)
For more details, see Practical English Usage Third Edition 73.