Before the Elves entered Middle-earth, the Valar entered Arda and also go through a period of aging at the end. They fade and become more impotent, as the shape and constitution of things become more defined and settled. The Elves would go through a similar route, though the difference is that the true life of a Vala is not corporeal and they were incarnate.
Time Scales
The Elves and mortals would also have their unique time scales based on their lifespans.
“The Quendi being immortal within Arda also aged with Arda as regards their hröar; but since, unlike the Valar, whose true life was not corporeal and who assumed bodily forms at will as raiment, their being was incarnate and consisted naturally of the union of a fėa and the hröa, this aging was felt chiefly in the hröa. This, as the Eldar say, was slowly ‘consumed’ by the fėa, until instead of dying and being discarded to dissolution it became absorbed and eventually became no more than the memory of its habitation of old which the fėa remained: this they became or have now become mostly invisible to human eyes.” (NoME, “Of Time in Arda”)
However, if we disregard the actual time, we would see the close resemblance of this process of the Elves and Men – reaching maturity at the age of 20, and then remaining in full physical vigor until the age of 60. At about 100 the Quendi would reach a similar stage as a mortal of full age and wisdom.
Rates of Growth
For the Elves, this would measure up to their own time scale of a year which is about 144 mortal years (MY). For example, when an elf-child grew to a maiden or young woman at “20 years old,” then she would be 2,880 at maturity. However, the Avari (unwilling) would age faster than initially planned – and start aging at a rate of 100 mortal years.
Later, those of the Line of Elros or the Half-elven line who chose to be immortal would also age at a rate of 100:1. For example, Elrond and Celebrían both aged at a rate of 100:1, and so would Arwen before marrying Aragorn and choosing a mortal life. Arwen would later join the Númenórean time scales based on her resulting age at that time.
Galadriel initially started out aging at a rate of 144:1 like any other elf, however, at the age of 26 (3744 years old), she would refuse to return west to Eressea and from then on she would start aging at a rate of 100:1.
However, after the Third Age, it is also said that the Elves would start to age even faster.
“It is said that after the fall of Sauron, and the beginning of the Fourth Age and the Dominion of Men, those of the Elves who still lingered in Middle-earth were again “quickened” to a rate of about 72:1, or in these latter days 48:1” (NoME, “Time-Scales and Rates of Growth”)
The speed also has nothing to do with the perception of time, as “when persons are fully occupied with things of deep natural concern and of delight to them, and are in great bliss and health, time seems to pass quickly and not the reverse.” (NoME, “Time-Scales”)
However, this would be true regardless of the time scale of the character, and could apply to Elves as well as Mortals.
Growth and Maturity in Elves and Men
The Elves would be vigorous in the beginning by the strength of their spirits, though they would eventually age. However, this aging that they experience is slow compared to mortals. But in the earlier days they would be as physical as Men, in that they would reach maturity at around 20 years old, and would remain in full physical vigor from the ages of 20 to 60. This would be the normal time for marriage and children.
The key difference between the Elves and Men is that unlike that of the Men, the fėar, or spirit of the Elves do not cease to be able to grow, and they would constantly be able to increase their knowledge and wisdom, though the later Elves, or the Elves from Second Age and beyond, did reach a stage where their memory starts to be a burden.
Thus, one might assume they move slower than Men. However,
“…the Quendi did not and do not ‘live slowly,’ moving ponderously like tortoises, while Time flickers past them and their sluggish thoughts! Indeed, they move and think swifter than Men, and achieve more than a Man in any given length of time…
*But not on a wholly different time scale. Thus to a Man Elves appear to speak rapidly but clearly [unless they slow down their speech for the Man] to move quickly and featly [unless they are in urgency] and only their thought, perception and reasoning seem normally beyond human speed.” (NoME, “Time-Scales)
They would have more energy than Men, causing them to take longer to expend – making their longer lifespans helpful for their desires.
Time for Marriage and Children
And lastly, the Elves would have more control over the events of the body and direction of the uses after reaching maturity at 20. For example, they can postpone marriage and also children (within marriage) while being occupied with pursuits that absorbed them, or because they did not find the desired spouse (the right person) or in times of trouble, wandering and exile.
Men do not have this, though it might not mean that they are forced into life events but they would have to work with the time scales they are given while the Elves would be able to adjust as needed based on their lives. For example, during the March of the Elves, there were virtually no marriages and children occurring at this time.
However, this postponement also affected the time when the body was in full maturity. Similar to mortals, the Elves would only have one period of bearing children which is typically during the time when they would be in full physical vigor.
“It might occupy from 12 to about 60 years (occasionally more). The children numbered usually 2, 3, or 4. One was exceptional, and could be due to different causes: for instance, the separation of the spouses, as in the case of Idris, daughter and sole child of Turgon of Gondolin whose wife Anairë of the Vanyar would not go with the ñoldor into exile, but remained with Indis (also of the Vanyar) widow of Finwë.’…In other cases the spouses (one or both) might not desire more than one child. This was rare, and in the histories of the Elder Days occurred only when some child of exceedingly great qualities was born which (as the Eldar say) demanded far more of the vigor and life of the parents than a normal child….A greater number than four was rare, though in the early days of the full vigor of the Eldar five or six children are recorded to have been born to one pair of spouses. Seven was wholly exceptional, and indeed among the High-elves only the case of Feänor was recorded.”
