That was over 31 years ago in 1990.
Today he is 59, and has starred in 51 movies in total, 35 since Back to the Future Part III was released.
In Back to the Future Part III, I think Michael J. Fox looks:
Back to the Future Part III scores 7.2 out of 10 on The Movie Database.
Michael J. Fox's first acting role was as 'Scott Larson' in Midnight Madness, released in 1980 when he was 18.