Numenorean Aging

[Sophia the Thunder Mistress]

How fast did those of Numenorean descent age at the time of the War of the Ring?

Some facts:

Denethor is just one year older than Aragorn, yet he's described as an old man while Aragorn seems in his prime.

Denethor didn't marry until age 46. Was he old when he married? Or was he aged prematurely by his stress and despair?

Finduilas, his bride, is 26.

Aragorn is 88 at the time he takes the throne in Gondor- as yet unmarried. I realize that Aragorn's longevity was rather exceptional for his time period, but it was also said that the blood of Numenor ran nearly true in Denethor, and he aged much faster than Aragorn.

Now the point. I need to know when "youth" ends and "middle-age" begins, for one of the line of the Stewards.

Would it have been exceptional for a "young lady" in her 40s to still have been considered a "young lady" or would she have reached Old Maid status by that time?

Sophia