Indiana Jones and the Idol of Eternal Youth

When is old too old? The perceptions of the last Harison ford Indiana Jones film were that Ford was too old to play the role. According to our cherished memories, yes, he was.
But why can’t we let our heroes grow old?
Do we hold to a belief of eternal youth that is offended when we see our action heroes become slow and weak?
Surely we can believe, as Indy did, that there’s life in the old dog still?