who are the nazgul?

[mhagain]

Originally Posted by Zigûr

I suppose it depends how long it took for them to become wraiths, because 2251 is only 30 years after the reign of Tar-Atanamir when the tribute was exacted and 222 years after his reign began. If they received their rings during the tribute period, ie during the reign of Tar-Atanamir at some point, that's not that much time for a Númenórean to exceed his natural lifespan. But I suppose it could be enough depending on how old they were and how quickly the Rings worked.
The Númenóreans had been settling Middle-earth during the reign of Tar-Minastir, Tar-Ciryatan's grandfather, however, which was still about a century after the War of the Elves and Sauron, so there were plenty of opportunities when Sauron might have been dispensing Rings.

This is an interesting question, but I don't think you can set a fixed time from receipt of a Ring to becoming a Ringwraith.

Gandalf's words to Frodo in Shadow of the Past are the best indication I can find:

A mortal, Frodo, who keeps one of the Great Rings, does not die, but he does not grow or obtain more life, he merely continues, until at last every minute is a weariness. And if he often uses the Ring to make himself invisible, he fades: he becomes in the end invisible permanently, and
walks in the twilight under the eye of the dark power that rules the Rings. Yes, sooner or later – later, if he is strong or well-meaning to begin with, but neither strength nor good purpose will last – sooner or later the dark power will devour him.

From this it seems to be the case that it's not exceeding your lifespan that makes you a wraith, it's using the Ring often. Also, if you're well-meaning or if you're particularly strong, the process takes longer.

Smeagol/Gollum had the Ring for about 600 years, but "it was long since he had worn it much: in the black darkness it was seldom needed" so he didn't become a wraith. As Hobbit-kind he was more resilient too, of course. Bilbo had it for 60, and was already starting to feel "all thin, sort of stretched, if you know what I mean: like butter that has been scraped over too much bread". Also a Hobbit, also more resilient.

I think taking a median-point in Atanamir's reign and assuming that they used the Rings a lot, 100 years would be plenty of time for an already corrupted Man to become a Ringwraith. A total guess of course but it seems reasonable.