This is discussed in great depth in HoMe X, Morgoth's Ring. To make a long story short, Tolkien originally decided that Elves were reborn in their descendants. In this version, Glorfindel would have had new parents and gradually remembered his former life. Tolkien later decided that this was inconsistent with the metaphysics of Arda, however. He changed the mythology so that Elves are not reborn, but reincarnated. Since each fea (soul) corresponds precisely to a single hroa (body), the Valar are capable of making an exact replica of the body of an Elvish soul. So in the later version, Glorfindel appeared as an adult.
Elves were, naturally, reincarnated in Valinor. HoMe XII, The Peoples of Middle-earth, discusses Glorfindel's return from Valinor. It seems that Tolkien's latest idea was that Glorfindel was sent, like the Istari, to aid the free peoples of Middle-earth against Sauron; there are varying accounts of when exactly he returned, but it seems to have been during the Second Age.
|