The incongruities that occur when an aging actor plays a character who is specifically not supposed to age: vampires, robots, long-life-spanned fantasy creatures, someone who plays a character with a clear, if Vague Age, for too long, and so forth. Most situations are resolved with the MST3K Mantra, but it still can be the cause of some behind the scenes hand-wringing. Contrast with Not Allowed to Grow Up, where there is no in-story reason for the character's appearance to remain the same.
- Rimmer from Red Dwarf, as a hologram, is supposed to retain the same appearance from the beginning of the series. However, Chris Barrie naturally and visibly ages over the 20 years of the show's run. Interestingly, there is also an episode that features a fat, balding Future Rimmer... right after one that shows Rimmer aging 600 years without major change.
- Brett Spiner claimed that one of the reasons he pushed for Data's death in Star Trek: Nemesis was that he increasingly felt he could not keep playing the ageless robot as he was reaching his 60s.
- David Borenaz, already a victim of Dawson Casting ages from his late twenties to late thirties throughout his appearances in the Buffy Verse, with flashbacks throughout showing that he looks the same in the past, while always reflecting his future appearance. Considering that he fills out considerably from season to season, this gets kinda odd.
- James Bond who, despite his movies forming a loose continuity, each actor who portrays him has a time limit on how long he can play the relatively young secret-agent. Thus, he can go from the 58 year-old Roger Moore in A View to a Kill to the 43 year-old Timothy Dalton in The Living Daylights, while secondary characters like Desmond Llewelyn's Q grow older.
- Elves are supposedly ageless. Yet not even the good CGI could fully hide that Hugo Weaving as Elrond had gained ten-years between The Fellowship of the Ring and prequel-movie The Hobbit.
Hello, Unknown Troper. You'll need to get known to lend a hand here.