Well, Barenziah isn't youthfull....but she's not a doddering old woman, either. Her mind is still very sharp (Which is to be expected of the woman who birthed Morgiah and Helseth...

) and I bet she's still fairly strong in body.
And Elves mature at the same rate as humans. They just age alot slower. And some dunmer due to various variables (quality of life, disease, injury, enviroment they work in, their family's medical history) have short lifespans.
