Jonny Lee Miller was 8 in Doctor Who: Kinda when he played the character 'Child'.
That was over 42 years ago in 1982.
This was his first recorded movie acting credit (although may not technically be his first actual acting role).
Today he is 51, and has starred in 33 movies in total, 31 of those since Doctor Who: Kinda was released.
In Doctor Who: Kinda, I think Jonny Lee Miller looks: