Like my grandmothers high school history teacher could be marry my son.
Creepy.
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.
FWIW, Elven childhood and growth was actually also much longer than human childhood, but it was quick in the eyes of the Elves.
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).
Yes, unfortunately we don't have more detailed portrayals since those passages in The Silmarillion are very brief.
The reason you would not write a scene with your ultimate villain on the toilet is the same impulse Tolkien may have felt here.