Rosamund Pike was 18 in A Rather English Marriage when she played the character 'Celia'.
That was over 25 years ago in 1998.
This was her first recorded movie acting credit (although may not technically be her first actual acting role).
Today she is 45, and has starred in 43 movies in total, 40 of those since A Rather English Marriage was released.
In A Rather English Marriage, I think Rosamund Pike looks: