Answer:
There are severel answers for that question that could be the answer you are looking for. In The Alvin Show, Alvin is 5, Theodore is 8, and Simon is 12. In the show Alvin and the Chipmunks, Theodore is 8, Simon is 8 1/2, and Alvin is 9. In the movie Alvin and the Chipmunks, Theodore is 6, Alvin is 8, and Simon is 12. And lastly, in Alvin and the Chipmunks: The Squeakquel, Theodore is 10, Alvin is 14, and Simon is 17. Hope I helped!