Something I found in the UT (which I'm re-reading for the nth time
) regarding the lifespan of Numenoreans, this is mentioned in 'the line of Elros';
This first one is actually from the Akallabeth which said the line of Elros "had long life even according to the measure of the Numenoreans". It also talked about the "end of vigour" (which came before the waning of their lives), stating that the descendants of Elros began to feel the end of their vigour about the 400th year or slightly earlier, whereas those not of that line felt it about their 200th year, or slightly later.
Its also mentioned in later writings that people of Numenor had a lifespan five times the length of other men (or three times the span, as is mentioned in Appendix A of LOTR), but this doesn't make such a clear distinction between the royal line and the 'plebs', as Elmo so beautifully put it
, saying only that the Royal line had a tendency to live to a greater age.
So it seems like allot of things, Tolkien was somewhat undecided in the final finished details!
