Real age of Mary Steenburgen in Back to the Future Part III
In the movie Back to the Future Part III, Mary Steenburgen was:
36 years old
That was the real age of the celebrity according to our calculation.
The calculation of the shown age took into account the first day of the year in which the movie Back to the Future Part III was released:
January 1, 1990
And the day in which Mary Steenburgen was born:February 08, 1953
Since movies usually don't take more than one year to be released since the beginning of the filming process, Mary Steenburgen may have been one year younger or one year older than the shown age while some scenes of the movie were being filmed.