Rebecca De Mornay was 21 in One from the Heart when she played the character 'Understudy'.
That was over 42 years ago in 1982.
This was her first recorded movie acting credit (although may not technically be her first actual acting role).
Today she is 64, and has starred in 49 movies in total, 46 of those since One from the Heart was released.
In One from the Heart, I think Rebecca De Mornay looks: