I'm having a hard time even believing you have to ask.
Hey, there's no need to be like that. It was a genuine question.
I probably could fill a whole thread with examples if this was something I studied extensively, but just off the top of my head we have invented a whole new category or stage of human life - adolescence.
This was hardly an invention of the past 150 years. It's been a natural progression tied to the development of the middle class and the transition from feudalism to mercantilism and then capitalism. Also, it is false to claim that the age of majority went totally unchanged prior to the last few centuries. During the early medieval period, yes, there was essentially no "transition" between infancy and adulthood--children were either non-persons, or (roughly around ages 10-14) adults-with-little-experience. By the 11th century, however, legal ages of majority in many places were 21--the age at which someone (usually the male heir but not exclusively) could inherit property aka the right which defined free persons, at the time--and by at least the mid-1400s, this meant people who could vote (the "40 shilling freeholders"). This remained pretty much constant for the entire medieval, Renaissance, and Victorian periods--in the US, the voting age was 21 until just the past century.
There has long been an idea that, even if someone were expected to be
responsible for themselves, they weren't persons with the full suite of legal rights until they achieved a higher age. To say that we "invented" adolescence from whole cloth is an exaggeration...to say the least. Yes, we conceive of childhood and adolescence differently now--much differently!--than the peasantry did a thousand years ago. But (a) the difference is primarily cultural, (b) it very much coincides with the expansion of economic opportunity to a larger fraction of the population (as I said above), and (c) it isn't nearly as dramatic as you're characterizing it to be.
Yet my own grandmother married my 22 year old grandfather when she was 16. I've had modern persons call that "sick" and "despicable" and treat that as a violation of a major taboo, yet merely a few generations ago that was normal.
The "modern persons" you're talking about need to rethink their positions. This is not only legal in most civilized nations (with parental consent, in some cases), but it wouldn't even be violating consent laws if they had had a physically intimate relationship. Marrying at 22 is hardly unusual; marrying at 16 is young, more or less bare-minimum in modern times, but hardly a profound transgression. (Also, it sounds like they stuck it out for the long haul--good on them.)
The entire 'youth revolt against the older generation' thing we treat as normal would have been basically impossible at an earlier time when you were entering adulthood at 13 and into a job at 10. <snip> That sort of mingling of generations was normal.
Sure, that's a very different experience than what we have now. How is it a difference of
personality? That's the word that was used, after all. We're talking about enduring aspects of a person's identity, not about the degree of separation that inspires a feeling (or mood, at the most) of homesickness. With the existence of magical communication, it's trivially easy (in comparison to...anything prior to the last century) for a fantasy character to get a message to someone if they have even the foggiest idea where that person is, and the level of "technology" is, again, a cultural thing rather than a biological thing.
A mere 3 or 4 generations ago, a child of 10 could not wait to assume the mantle and trappings of adulthood. Now, a man or woman of 20 fears them and often desires to postpone them as long as possible.
Hyperbole, and not even fully accurate. Often, a child of 10 did
not want to assume that mantle and trappings--they
had to because it was the only way to make sure the family survived. And there are still
plenty of modern teenagers who cannot wait to escape their parents. My sister, for example. "Fearing" the change? Hardly. Most kids are thrilled with the thought of the freedom they'll get--especially if they haven't had to get a job prior to 18. The "fear" usually only settles in once they realize they can't go back to all the lovely things that childhood had...which I have no doubt many a medieval person felt too, now and then!
Imagine how many someone that lived for 1000 years might have. We don't even have the vocabulary for it. We can't even discuss it without inventing a language.
That's...no, we absolutely have vocabulary for it. You just did it yourself (though I cut it out). I could even make a solid, if modern, analogy: To an elf, things like trees and rivers (but not things like mountains, coastlines, forests-as-a-whole, etc.) are like musical genres, or even individual popular artists, possibly actors as well. You can't see them changing moment-to-moment, but anyone who pays a moderate amount of attention can see the patterns. Do we decide, "Eh,




it, music will change in 10 years, there's no point in writing this song
now."?
And against your claim of the "not seeing the permanence of nature," I respond with both the things I've already said and more. The stars might,
barely, perceptibly change within a single elf's lifetime...but a number of astronomical phenomena that recur well beyond a human lifetime would occur many times for an elf. All sorts of cyclical things would happen, over and over and over again; this is a perfectly reasonable justification for a belief in the uniformity of nature, a belief that while things may change, they always return to what they had been or something indistinguishably different. And then continents and climates, in general, would remain unchanged, as would mountains--deserts
could change, but that would be slow enough to be akin to a tree for a human--you come back a couple centuries later and "man, things
changed while I wasn't looking!"
Now, with all of that said? It honestly sounds like you, and others, seriously want people to never play non-humans. I have to maintain a persona that is
actively outside the experience of human beings, at all times, invasively inserting as many possible points of divergence, just to be
allowed to play a Dragonborn or a Tiefling in your campaign? Sorry, not interested. I play games to have fun and experience interesting stories, not to have someone tell me that I'm not making my pretend elf
pretend enough.