Questions of social norms are always reduced to one question: What is biological and what is constructed
Me personally, I think that social norms in regards to sexuality change based on both the environment and biology people find themselves in. Back then in the 2nd century when people married at age 12 - 16 and life expectancy was low with people dying in their 40s, with no birth control, of course it made complete logical sense to not have pre-marital sex, stone people who did as a deterrent. You risk impregnating women who aren't ready to start a family, spread diseases everywhere, etc.
Nowadays, we have birth control and abortion; sex has very little risk and a small risk in diseases. Our life expectancy in the West is in the late 70s, so people have much longer time before settling down and starting a family. And our biology has not caught up. We still have extremely reproductive urges that people back then did.
Society has adapted and now it's an expectation of society, informally of course, to have sex in order to get experience, because there's little immediate risk in doing so and it's unnatural biologically to not have sex in your teens.
I don't think that cultural changes, which are accepted en masse by people, happen arbitrarily, randomly, without purpose.
Society will NOT fully accept transgenderism naturally as it exists now, because it's not natural. Injecting estrogen and putting on a wig does not make one a biological woman.
We have accepted a "extreme whoredom" phase of "love" as a society because it's natural.
Well even if I agree with you, something being natural doesn't make it good or valuable. Actually it's nearly always exactly the opposite, which is why our natural behavior needs to be restrained if civilization is to even exist at all, much less any advancement. You're definitely correct about the implicit expectation to get sexual experience as a teenager. But to what end? To have a lot of meaningless sex with essentially random people? Or to prepare for your inevitable failed future relationships? I struggle to see a purpose to any of it, and it seems horribly unappealing. But I suppose I'm in the minority there, most non-incels seem to be mostly okay with the current state of affairs. However it's shit like this which makes me wonder whether or not I'm sort of alien disguised as a human, or if there is some considerable distance which separates me from other people. Although who knows, maybe I'm just autistic.
If I engage with these thoughts, I then wonder if I'd even be better off if I weren't incel. I mean most of the stuff that bothers me is memories of being treated like garbage and rejected by other people. Obviously I have desires for physical closeness and sex which I can't fulfill, but it's not like these would ever really cease to bother me even if I were a normie. The desire doesn't go away the more you fulfill it, if anything it's the other way around. Otherwise people would be content in the knowledge that they could get these things if they wanted them, or that they've had them in the past. But that's just not what we see. So as far as I can tell, the only people who get to feel any measure of lasting satisfaction are those who can satisfy their desires constantly, or those who have reduced them to the point where they aren't really a bother, and both are in the extreme minority. At least among men anyway, as the former is sort of common for women. Although when you consider that women are genuinely Chadsexuals, it's probably at least somewhat less common than we think, especially for older women.
When you set aside sexual deprivation and skin hunger, most of the pain caused by inceldom is constructed within our own minds. We might think that we should be doing something because other people are, or that we're worse off for being incel than we really are. If you're a khhv, the knowledge that nobody ever told you that you're good enough is ever-present. Once you accept that even if you got to fulfill your urges a few times, that the problem would still be there, it becomes clearer that a lot of our problems come from not being validated by other people, along with the aforementioned physical deprivation which isn't even unique to us. The thing is, you don't actually have to care about getting validation from women or really anybody else. You can stop caring about validation entirely, or if that doesn't work, then there is nothing stopping you from fulfilling this subjective need artificially, since you've already accepted that it's a mental construct anyway, albeit one that you didn't create intentionally.
What I'm getting at is that the concept of developmental milestones is subjective, and the reason is because the failure to meet milestones only exists when we examine our experiences in contrast to those of others, and they change depending upon the context. Just because you can explain a series of behaviors through genetic/environmental determinism or evolutionary biology, well it doesn't mean that our perception of failure is any less subjective. I suspect that people tend to project purpose and intent upon that which has none. Or alternatively, even if there is a purpose behind the natural world, I would argue that it's absolutely malicious and not worthy of respect. Either way, we don't actually have to care about whether or not we succeed in satisfying our urges, and we don't have to discern whether or not something is natural to decide if it has any value. Now I'll stop rambling as to avoid making this wall of text even longer.
