CORRECTION

Actually, the DC letter printed below couldn't have been that first one after all as a quick read makes mention of the fact that Superboy's parents look younger due to a serum from another dimension. Clearly this is a reference to a SUPERBOY story that appeared in, I believe, late 1967 or early 1968 in which some enterprising other-dimensional alien is using the Boy of Steel's real life as the basis for a TRUMAN SHOW type series. When told that his Q ratings were skewing too old because of the older "actors" playing the Kents, the sneaky fellow, realizing that he can't replace them, sends a youth potion their way and its effects are (conveniently) irreversible