The "Elven Lands" are a demiplane, out of phase with the rest of the world in time. For every day that passes there, 5 pass in the outside world. Growing up there means that you'll stay young for five times as long... which is the secret to the elves' longevity in the outside world. And to elven power; there are a few very, very old and very powerful elves around. God wizards and the like.
But the kicker is, you have to grow up in the elven lands to be properly instilled with longevity by them. So elves are rarely seen in the outside world until they're 20... or 100, depending on how you're counting.
Where the rest of the world and the elven lands meet stands an elven city, in phase with the rest of the world. Very, very few non-elves have ever passed beyond it into the elven lands proper. Those from the rest of the world who are viewed as friendly may enter the trading quarter of the city. But it's rare indeed that they'll ever see an elven child.
The elven demiplane is actually a fragment of what was once their world. The Drow live on another fragment; unlike the elves, they take back slaves. However, these slaves age and die rapidly, by how time runs in Drow lands, unless brought over as children; as do all who enter the elven lands. Drow thus are far more likely to take children as slaves than adults. Taken at the right age, these children will age "fast" as time is measured in the Drow lands, yet slow down in aging as adults even while not fully psychologically developed. A very few have escaped, to find a world where centuries have passed while they were away for decades.
The rest of the former world of the elves was destroyed in a long-ago mage war. The main elven population and the Drow are the remnants of the two main factions.
Wood/wild elves are the refugees of this conflict, and their aging is only slightly slower than human.
If they have to have dealings with those from the outside world, the very old elves with centuries of experience and arcane knowledge which form the basis for their power will sometimes disguise themselves as "elven gods". Over the centuries, this has led to a conjecture, which in turn has led to a mythology among some of the other races that the elves themselves have the potential to attain divinity.
The main body of elves trade, in the city which straddles the worlds, with fine fabrics and other consumables, many of them luxury items, which seem to stay fresh and new far longer than those made in the prime material plane. Elven weapons and metalwork are also held in some esteem, since they seem to keep their edge and form longer, with less maintenance. In return, the elves are only interested in items made from the more permanent things from the prime material plane, such as gold, stone, ceramics etc. Almost anything else will decay far too fast after being taken between worlds.
The light's dimmer in the elven lands. Hence the eyesight thing. Maybe the war even damaged their sun, or maybe their world floats at a greater distance from their sun, but in a nebula which provides a permanent glow...
The drow lands have broken off from the main elven world. Their surface is an inhospitable place, without breathable atmosphere, and they therefore live in the interior, with the only gravity being that they create by their sorceries. (Effectively making these Drow moon-Nazis).
Relations between the main elves and the wood elves are friendly enough... but the latter cannot cross back, unless as babies, for fear of aging; they're now time-synched with the prime material plane.
A diet consisting largely of foodstuffs from elven lands has the side effect of very slightly delaying the aging process for those who consume it. Only by a factor of, say, 1.5 or so; but even this is regarded as a precious boon by the wealthy and privileged.
What this means for adventurers/plots
- A first level elf would have only recently attained the right to travel to the city or beyond, and could have left the city for practically any reason; the world outside would likely be rather strange to him or her, being as it's a different plane and all.
- A mid-level or high-level elf might have done their other adventuring a long time before, then gone home to raise a family, and return to a world which had changed by, say, 150 years while they lived for 30.
- Or they might have lived in the outside world for centuries, and seen nations rise and fall.
- Diplomatic negotiations with the elves can take a long time to resolve, if it's something for which those who live within the elven lands, rather than the city, would need to be consulted
- Adventurers wishing to visit the elven or the drow lands would be well advised to keep their visits brief, and not to visit while pregnant. If they stay for years, they'll grow old uncomfortably fast.