Question

Which line best highlights Bilbo Baggins’ unusual youthfulness?

When Mr. Bilbo Baggins of Bag End announced that he would shortly be celebrating his eleventy-first birthday with a party of special magnificence
The riches he had brought back from his travels had now become a local legend . . .
At ninety-nine they began to call him well-preserved; but unchanged would have been nearer the mark.
Mr. Baggins was generous with his money, most people were willing to forgive him his oddities and his good fortune.

Answer 1

"At ninety-nine they began to call him well-preserved; but unchanged would have been nearer the mark."

Explanation: this line directly emphasizes that, despite his advanced years, Bilbo appears unusually unchanged and youthful.