Movie-Theodred is definitely younger than Book-Theodred; he is 20-25 years old.
The above picture is the only Theodred photo available on the 'net. Do you notice something? Yes, we do not see a scene of the movie! That means that we will probably get to see how Theodred was wounded in the extended version of "The Two Towers"!
He was strong in life. His spirit will find the halls of your people
In the book Theoden and Theodred didn't seem very close to me while in the movie we actually see the King mourn.
In the movie we also see a bond between Eowyn, Eomer and Theodred. They seem familiar together; like best friends.
Another thing that should be mentioned is Brego, Theodred's horse; Brego is the name of the second King of Rohan, by the way.
Brego, the horse, however, went wild after his master's death and did not allow anybody to touch him until Aragorn arrived at Edoras and talked to him about it ...
The greatest line on Theodred in the movie was what Gandalf said, however:
