Richard Powell

 played Irving Bates, Jr. in the sixth season episode, Just a Kid Again (1970).

Identity
The Internet Movie Database lists Ricky Powell as playing this role. This is incorrect. Ricky Powell is a different actor who appeared in two other Bewitched episodes - Season Seven's, Mary, the Good Fairy (1971) and Season Eight's, Samantha's Magic Sitter (1972).

Poster GaryB on Harpie's Bizarre mentioned speaking with Ricky Powell about the matter and Ricky confirmed he did not play Irving Bates, Jr. GaryB also mentioned in the same post that he could not find anything about Richard Powell.

Likewise, as of December 30, 2021, Bewitched Wiki could not find anything on Richard Powell.

Source
GaryB. "Just a Kid Again Actor", message board reply, Bewitched@Harpie's Bizarre, February 28, 2015. Retrieved on December 30, 2021.