Who is the Mouth of Sauron?

[Maedhros]

Who is the Mouth of Sauron?
From the LOTR: The Black Gate Opens

At its head there rode a tall and evil shape, mounted upon a black horse, if horse it was; for it was huge and hideous, and its face was a frightful mask, more like a skull than a living head, and in the sockets of its eyes and in its nostrils there burned a flame. The rider was robed all in black, and black was his lofty helm; yet this was no Ringwraith but a living man. The Lieutenant of the Tower of Barad-dûr he was, and his name is remembered in no tale; for he himself had forgotten it, and he said: ‘I am the Mouth of Sauron.’ But it is told that he was a renegade, who came of the race of those that are named the Black Númenóreans; for they established their dwellings in Middle-earth during the years of Sauron’s domination, and they worshipped him, being enamoured of evil knowledge. And he entered the service of the Dark Tower when it first rose again, and because of his cunning he grew ever higher in the Lord’s favour; and he learned great sorcery, and knew much of the mind of Sauron; and he was more cruel than any orc.

Age of the Mouth of Sauron:
According to LOTR: Appendix B

In the Secong Age: c. 1000; Sauron, alarmed by the growing power of the Númenoreans, chooses Mordor as a land to make into a stronghold. He begins the building of Barad-dûr.
But it was stated that he entered to his service when the Dark Tower first rose again.
In the Third Age: 2951; Sauron declares himself openly and gathers power in Mordor. He begins the rebuilding of Barad-dûr.

What is a Black Númenórean?
The Black Númenóreans were the ones who were deceived by Sauron when he was captured in Númenor. They took to the worship of Morgoth and they built in Armenelos a mighty temple for him.
From The Published Silmarillion: Of the Rings of Power and the Third Age

Now Sauron prepared war against the Eldar and the Men of Westernesse, and the fires of the Mountain were wakened again. Wherefore seeing the smoke of Orodruin from afar, and perceiving that Sauron had returned, the Númenóreans named that mountain anew Amon Amarth, which is Mount Doom. And Sauron gathered to him great strength of his servants out of the east and the south; and among them were not a few of the high race of Númenor. For in the days of the sojourn of Sauron in that land the hearts of well nigh all its people had been turned towards darkness. Therefore many of those who sailed east in that time and made fortresses and dwellings upon the coasts were already bent to his will, and they served him still gladly in Middle-earth. But because of the power of Gil-galad these renegades, lords both mighty and evil, for the most part took up their abodes in the southlands far away; yet two there were, Herumor and Fuinur, who rose to power among the Haradrim, a great and cruel people that dwelt in the wide lands south of Mordor beyond the mouths of Anduin.

In 3262 S.A.; Sauron is taken as prisoner to Númenor; 3262-3310 S.A. Sauron seduces the King and corrupts the Númenoreans.
3320 S.A.; Sauron returns to Mordor.

There are two possibilities that I can see. If the Mouth of Sauron is a black Númenórean, then he could be one that escaped the destruction of Númenor by going to either Pelargir or Umbar and entering openly into the Service of Sauron in 3320 of the Second Age.
Or, he was a descendant of Black Númenóreans, and entered his service in 2951 of the Third Age. It is in 3019 of the Third Age when Sauron was defeated.

In Scenario A, if he entered into his service in 3320 of the Second Age, by the time of the defeat of Sauron, he would have been 3341-3320 = 21 + 3019 = 3040 years in the service of Sauron.

In Scenario B, if he entered into his service in 2951 of the Third Age, he would be: 3019 – 2951 = 68 years old in the Service of Sauron.

If Scenario A is correct, then it would be coincide with the fact that he was an Original Black Númenórean, but the problem with that is how do you explain the fact that he lived for over 3000 years, and was not a ringwraith? He was a sorcerer, and he knew much of the mind of Sauron, but could he had learned enough to live that long? Granted that if you lived that long, it is possible that you will forget your name.

If Scenario B is correct, then the Mouth of Sauron would have been in the Service of Sauron for 68 years and because he was a descendant of Númenóreans, it is possible that he already was 100 or 200 years old. Would 168 or 268 would be long enough to forget your own name?