[shiroiuma]

I don't see why that's "creepy", just because it seems weird to you and too hard to contemplate. In a future world where people stop aging at adulthood, this would be normal: everyone would seem to be 25 or 30, and there could be huge age-gaps in relationships. Why is that wrong?

In practice, however, age itself would probably become valuable on the dating market. Since people would look young indefinitely (until some tragic accident), youth probably wouldn't be valued any more, but quite the opposite: older people would have valuable and interesting life experience, and probably better finances too thanks to compound interest. So your grandmother's high school teacher might not be that interested in your son because he's too young and inexperienced.

Another thing that would likely happen is that relationships would no longer be assumed to be life-long. We already have accepted divorce pretty well these days, but in the ageless future, it'll probably be normal for marriage-type relationships to have pre-agreed time limits.

[fmajid]

Neuroplasticity, and the loss thereof with age would cause older elves to get quite ornery and unsociable. The only active elvish couple depicted is Galadriel and Celeborn.

[Amezarak]

Tolkien actually wrote a lot on this sort of stuff, you can find it in the Nature of Middle Earth. Elven marriages are, however, lifelong. Even the death of a spouse did not permit remarriage, except in on very exceptional case.

FWIW, Elven childhood and growth was actually also much longer than human childhood, but it was quick in the eyes of the Elves.

[gpderetta]

> Even the death of a spouse did not permit remarriage

that's because on death elves reincarnate in Valinor. The exception was given when the spouse refused to reincarnate (and a lot of pain resulted form that incident).