The Actor feat (PHB, p. 165) says:
You can mimic the speech of another person or the sounds made by other creatures. You must have heard the person speaking. or heard the creature make the sound, for at least 1 minute.
If a player learns this feat at 8th level, can they mimic speech they heard back when they were 1st level (when they did not have the feat)?
What about a speech heard 200 years ago, when they were but a small elven child?
RAW, I think it's allowed. And I don't think it breaks the game to allow it. But I'm curious if there are any aspects of this that I'm missing. I would assume that for the 200-year-old speech, that it would at least have to have been memorable in some way! :-)