From 1964 to 1965, Rettig co-starred with another former child actor, Tony Dow, in the ABC television soap opera for teens, "Never Too Young". With the group "The TR-4", he recorded the song by that title on the Velvet Tone label. While he was the TR-4's co-manager, he did not sing with them. Rettig only co-wrote the song in hopes that the TV soap would use it as the series' theme. The record was produced by Joey Vieira, who under the stage name Donald Keeler played Rettig's sidekick Porky on "Lassie". Producers of "Never Too Young", however, chose not to use it. Rettig was subsequently cast as Frank in the 1965 episode "The Firebrand", of the NBC education drama series "Mr. Novak", which starred James Franciscus.