"I once aged 90 years old in one episode"

DeForest Kelley's quote is most likely describing his function as Dr. Leonard "Bones" McCoy in the original Star Trek series. In the episode "The Deadly Years", Dr. McCoy is exposed to an odd radiation that causes him to age rapidly. By the end of the episode, he is 90 years of ages. This quote is likely an amusing recommendation to the episode, as it was a special experience for Kelley to play a character that aged so quickly. It also speaks to the power of the show's unique effects, as Kelley was able to convincingly represent a much older version of his character. The quote is a testament to the program's capability to develop a credible and immersive experience for its viewers.