Considered the best episode of the animated Star Trek, “Yesteryear” by D.C. Fontana was about Spock going back in time to give his younger self wisdom.
However, Fontana, when writing for Land of the Lost reused this exact same premise in “Elsewhen,” where a future, all grown up version of Holly goes back in time to advise her younger self in a key crisis. It’s another example of how Land of the Lost (a much, much better show than Generation X’s misleading cheesy collective memory of it would have you believe) was a sister show to the original Star Trek. Among other things, the pilot episodes of Land of the Lost were written by Next Generation co-creator and original series writer David Gerrold.
Erica Hagen played the grown-up Holly in this episode. Later, she would play a phantasm of Will and Holly’s mother (in the only episode she is ever discussed), implying that Holly grows up to be physically identical to her mother.