I'm 25 and I require 8.5 hours of good sleep for optimal performance.

I did some benchmarking about three years ago by timing myself trying to solve similarly-challenging Sudoku puzzles in a Nintendo DS game. With good sleep, I'd consistently approach 14 minutes with zero mistakes. After about 2-3 days of not having good sleep, it would drop to 16-20 minutes with more mistakes. I would also consciously notice various effects like diminished memory recall, more stuttering, poor focus, etc.

I've also been hearing that the length of sleep required is typically reduced with age. I don't have any citation on this though, would love to read more on the topic if anyone has more insight.