In many of the comic future stories, Clark gets gray hair and looks older...but he's also functionally immortal. If you look at something like Kingdom Come, he looks like this:
Still healthy and in perfect shape...but grey hair less boyish looks.
Anyways, I enjoyed the story. I guess it might be different in the L&C verse since there are no other heroes. Lots of men and women hold on to great looks into advanced ages. Usually celebrities...but it can happen.