Josh Hartnett was 19 in Halloween H20: 20 Years Later when he played the character 'John Tate'.
That was over 26 years ago in 1998.
This was his first recorded movie acting credit (although may not technically be his first actual acting role).
Today he is 45, and has starred in 46 movies in total, 43 of those since Halloween H20: 20 Years Later was released.
In Halloween H20: 20 Years Later, I think Josh Hartnett looks: