In the book the Emperor is described as being in his early seventies yet looks no older than 35.
Yeah, I genuinely think this is just an unreasonable casting expectation. Personally I’m glad Denis/the casting director is ignoring this and just focusing on who is the best actor to bring the right qualities to the role.
Why is it unreasonable?
We’ve had plenty of actors in their mid twenties playing beings who are centuries or millennia old (vampires, LOTR elves, etc), so this wouldn’t be much of a stretch.
I will never watch the Dune adaptation I want, that is a fact.