In The Hobbit : An Unexpected Journey the 50 year old Bilbo Baggins is played Martin Freeman and when he gets to his 100's (at the start of the movie and in The Lord of the Rings) Ian Holm plays a older grey haired version of Bilbo. In the LOTR book it is said
Time wore on, but it seemed to have little effect on Mr. Baggins. At ninety he was much the same as fifty. At ninety-nine they began to call him well-preserved ; but unchanged would have been nearer the mark.
So, Shouldn't Bilbo still be the same young hobbit he was at 50?