Book 12 Peoples of Middle earth
Christopher T's ... Editing of his fathers work disagrees with both of your opinions that the maturity of an elf surpasses the expectation of human development.
As told in The History of Middle-earth and in Tolkien's Letters, Elves had a different life cycle from Men. Most of the following information strictly refers only to the Eldar, as found in his essay Laws and Customs among the Eldar, found in Morgoth's Ring.
[edit] Early life
Elves are born about one year from their conception. The day of their conception is celebrated, not the actual birthday itself. Their minds develop more quickly than their bodies; by their first year, they can speak, walk and even dance, and their quicker onset of mental maturity makes young Elves seem, to Men, older than they really are. Physical puberty comes in around their fiftieth to one hundredth year (by age fifty they reach their adult height), and by their first hundred years of life outside the womb all Elves are fully grown. Elven bodies eventually stop aging physically, while human bodies do not.[18]
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