Best young / best older fighters

Just curious to hear some thoughts. The most promising/best young fighter ever and the best older fighter ever. Older I would reckon Dan Severn would be hard to beat. That guy seems to have gotten better with time (not so sure about right now though of course), Don Frye seemed evergreen, what other are there? For young prodigies, Vitor Belfort of course would have to be thrown in the mix, BJ Penn I imagine wouldn't have been too bad.

Any additions?

Hendo? Phone Post