What are the age ranges for various generic age descriptors, eg, "ancient" "elderly" "old" "young"?

Obviously teenager is 13-19.

"Young adult" would start at 20, but where's the cutoff at the upper end? Similarly, what's the range for "adult", "old", "elderly", " ancient"?

If someone asks for responses from "old men", how do I know if it applies to me?