Christina Applegate was 37 in Alvin and the Chipmunks: The Squeakquel when she played the character 'Brittany (voice)'.
That was over 14 years ago in 2009.
Today she is 52, and has starred in 50 movies in total, 15 of those since Alvin and the Chipmunks: The Squeakquel was released.
In Alvin and the Chipmunks: The Squeakquel, I think Christina Applegate looks: