Board Thread:Suggestions forum/@comment-88.117.41.142-20151221171736/@comment-26298013-20151224021407

Age has less to do with an Elf's power than does one, crucial factor: Whether or not they have ever lived in Valinor. Specifically, having lived in Valinor during the times of the Two Trees.

Galadriel lived in Valinor in the light of the Trees, and therefore has power. Same with Glorfindel. Elrond can grow as old as he likes, but without the Ring of Air he has less strength than Glorfindel. With that Ring and his own strength (The Halfelven are, for some reason, always strong in body, mind, and in Tolkien's "magic") Elrond is a formidable opponent.

Age does have two connections to Elven strength, however: As Elves age, they tend to tire of Middle Earth, become weary, and weaken. But only the oldest Elves, however, were old enough to have lived in Valinor and so only the oldest Elves have great magical strength.