Author has written 3 stories for Lord of the Rings.
Well... given the fact that I am terrible at updating, my info keeps going out of date, so I'm just going to ignore it...
So no one is confused in my stories, here are my general beliefs about elves:
1) Maturity: Elves grow mentally at the same rate humans do, but take much longer to grow physically. Therefore you can have an elfling as small as a five-year old who is able to read, write, and have the motor control of a teenager. However, since they are still coddled and spoiled (as all little kids are) they generally still act much like a little kid. Elves grow normally up until about 2 years old, then gradually slow down the process until, around the time they reach maturity, they grow so slowly that they do not seem to age at all, merely gaining an "ageless" look (hence the reason why elves always look youthful.) Elves reach their adulthood at the age of 144. I have read works where Tolkien said that elves reached adulthood between 50 and 100, and that the first elves tended to marry shortly after they turned 50, but I have also read accounts where it has been said that elves basically reached puberty at that age. I am inclined to think that, like in human cultures, the age at which one is considered "adult" has been pushed back. In many human societies thousands of years ago, people were considered adults and were married as soon as they hit puberty. Now it is significantly later. I assume that this happened with the elves as well. This is pure speculation on my part, but I think that once the elves truly started functioning as a society and pushing the age of adulthood past the age of puberty, it would have eventually developed so that an elf would be considered a full adult after they reached one yen. A yen is the equivalent of 144 years and is the most significant elvish unit of time. (Elves count in twelves.) Soooo, my thought is that they would take this important amount of time in an elf's life and make it the coming-of-age. :)
2) Groups: The elves were divided into three main groups when they were created: The Vanyar, The Noldor, and the Teleri. These three groups started across to Valinor, but some did not wish to go. These stayed behind and became what are now the Silvan Elves. On the Shores of the Sea, some of the Teleri remained behind. These became the Sindarian Elves. The Silvan Elves and the Sindarian Elves are not quite as wise and fair as those who sailed because they never saw and talked with the Valar, but they are still fairer and wiser than mortals. Eventually, some of the Noldor came back across the Sea, bearing some Vanyar and Teleri blood with them, and some mixed with the Sindar.
3) Looks: I envision the Vanyar as being golden-haired and green-eyed, the Noldor as being dark-haired and grey-eyed, and the Teleri as being Silver-haired and blue-eyed. Sindarian Elves, (being primarily Teleri) have mostly silver coloring, but also have some dark-haired elves and even a few blonde ones due to the Noldor elves that came back from Valinor. They mostly have blue eyes, but some have grey or green. Silvan elves, being a mixture of all three, can have a combination of any hair and eye color listed above.
4) Marriage: When Elves were first created, they usually got married not long after reaching their majority and typically had 3-5 children. The marriage united the souls of the elves, so that they were truly one. Elves only ever get married once (excluding Finwe, whom the Valar allowed to re-marry), because the bond between souls cannot be broken, even by death. As time went on, Elves began marrying later, taking more time to be sure that they wanted to be with their beloved for eternity, and because they wanted to spare themselves and their loves the possible heartache of losing their spouse in battle. The Valar also blessed them with fewer children, simply because Middle Earth no longer needed so many more to populate it.
5) Fading and Sailing: Elves can only die from serious injuries or from grief. When elves die, it is only their bodies. Their souls go to the Halls of Mandos, where they live on. When an elf chooses, he can forsake his body to travel to the Halls of Mandos in order to be reunited with loved ones. However, it is a grave sin to throw away the gift of the Valar in such a manner. Very few elves fade; those that do typically try to hold on for as long as they can until the pain becomes too much. Then, they either fade or travel to Valinor, where the Valar relieve the ache in their souls. Noldorian elves are able to return to Valinor at any time, since they came from there. They experience a constant ache, like homesickness, and typically only stay in Middle Earth because of an attachment to a cause, place, or person. Silvan and Sindarian Elves, on the other hand, do not experience any kind of homesickness because they were never in Valinor to begin with. Rather, they stay in Middle Earth because it is their home. They sail only when the call of the Sea is awakened in them. (How is different for every elf. Not all elves would feel the call upon hearing the seagulls, as Legolas did.) Once the call is awakened, however, it becomes a deep, intense longing, not allowing the afflicted elf any peace until they sail.
6) Rebirth: Because the souls of dead elves still live (albeit in Mandos' Halls), the Valar sometimes allow an elf who had paid for his misdeeds to be reborn instead of creating a new soul for the unborn body. The reborn elf only gradually regains the memories of his past life. This is a rare occurrence, however, as many souls do not wish to return to Middle Earth, preferring to linger in the Halls of Mandos, where they can be sure of peace and security. They are not ready to face Middle Earth with all its trials and face the reality of whatever happened to cause their own deaths.
7) How they are Different: Elves are taller than humans, but not ridiculously tall. I would guess an average male elf stands about 6'4, and an average female around 5'11. They are also faster, stronger, and more agile. They can go for days without eating or sleeping, and they heal much faster than men. Therefore, they can recover from injuries that would surely kill a man. (Though I have read nothing to make me believe that an elf can endure physical pain any more stoically than a man.) They can move soundlessly when they wish, and are so light that they can even walk on top of snow. Their senses are far keener than a man's, and they are able to hide themselves from the sight of all with ease. Elves have a great love for nature, especially the stars, so they are afraid when they are cut off from such things. (Hence their dislike of caves.)
Well, I hope no one was bored to tears by my slight (or not so slight) obsessiveness with elves. ;) I'll shut up about it now.