live longer than his Dúnedain peers?
I will need to do some individual research on the peers.
Clearly it's noted that the rulers of
Númenor became increasingly proud and decadent. Then of course they began to rebel against the Eldar and
Valar. It MAY have something to do with that. (A bad lifestyle kills...!

) But I speculate.
What
materials have you researched already that haven't answered the question, so I can avoid those in the search? I personally can't promise you an answer really 'quickly'... maybe a couple days.
And maybe some of our other members with a better or possibly mnemonic memory can help. I have only a semi-eidetic memory, which helps at times to be able to 'reread' images from pages, but when I haven't read the pages, or it's been awhile since I have, the images fade.
Of course, it is to be remembered too, that
Sauron deceived many of them in
Númenor, which is why they revolted in the end. This must have some consequence on their lifespans.
That said, so far all I've found is that the Dúnedain were granted many of the powers and skills of the
Elves, though not immortality, but were granted a lifespan "thrice that of mortal
men". (PoME)
More later.
Actually it seems their life-spans started to decrease even before Sauron's corruption of
Númenor.
We read this:
"By the 23rd Century, in the reign of Tar-Atanamir, the Dúnedain began to speak openly against the Valar. Soon the Eldar were estranged and the Hallow of
Eru neglected. Only
the Faithful (q.v.) remained loyal to the Valar and friendly with the Eldar. In succeeding generations the majority of
Númenóreans, known as the King’s Men (q.v.), abandoned the use of the Elven tongues, persecuted the Faithful, and lost the joy of life through the fear of death. The
Kings in 2899 began to take their royal names in
Adûnaic, and
the dwindling of their life-spans increased. In 3175 Tar-Palantir tried to return to
the old ways, but his reign was marked by civil war, and on his death in 3255 his nephew usurped the crown and became
Ar-Pharazôn."
Prior to this, they had become corrupted through their desire for more power, fear of death, and especially the desire for immortality.
Only the 'few faithful' who escaped the destruction of
Númenor seem to not have succumbed to finding their satisfaction in "lordship, ornate tombs, riches and revelry."
So it does seem their diminishing "graces" (including lifespan) are linked to their rebellion and turning from what they were given through Eru.
(More later if I find anything more conclusive.)