Right, it's more that our society has decided that humans have no value until they're at least 18 (hell, with college degree requirements that age is approaching 22), so we have to store them somewhere until then.
That's a nice way of looking at it, and I'm not going to argue against it per se, but a cynical part of me thinks there's simply more money to be made by pushing loans on young adults and then using them in the workforce.
US student loan debt is somewhere around $1.4 trillion. For comparison, mortgage debt is somewhere around $8.9 trillion. That's a pretty damn big market. [0][1]
If that education was free, I'd wholly agree with you that it's simply our society deciding this is for the betterment of all. But when you combine these two sources of debt (student loans so we can get jobs that afford us home mortgages) then we're looking at a new, weird, first-world form of debt bondage. [2]
Again, I realize that's a very pessimistic point of view. Will be interesting to see how the history books view it in years to come.
That's a better way to put it; we've decided that humans' lifetime productivity is usually maximized by putting off the requirement that they be productive until later in their lives.
Does it make your nebulous conspiracy theory more believable or less believable when you consider that the age of 18 is generally when people's bodies have reached full maturity?
Personally, if my 22 year old self travelled in time three years backwards to meet 17 year old me, and then travelled 20 years forward to present day to me current me, I have no doubt 18 year old me would the odd man out in this triplet.
18 maybe for physical appearance, but mental maturity and brain development completes in the early-mid 20s. I would definitely be the odd one out at my current age if I were stuck with 17 and 22yo me, unless you were just using physical appearance, in which case yeah, I guess 17 would stand out.
Mental and social maturity continues developing for most of your life. Different life stages have different common problems, and you need to learn different skills to solve them - or sometimes just to cope with them.
In the same way that there isn't much practical (i.e. economic) interest in tailoring schools and college classes to people with different daily cycles, there isn't much interest in teaching people about common problems ahead of time, or running some kind of continuous life challenges training that could potentially do a lot to improve life quality.
In my 50s, one of the common problems my friends have is dealing with parents who are either dying, recently dead, or have a terminal illness like Alzheimer's.
Of course that happens to younger people too, but there are actuarial peaks where it becomes massively more likely that you'll be dealing with a certain set of challenges in a certain decade of life.
There's shockingly little information around about some of these challenges. So it's incorrect to assume that the learning ends after school or college.
You won't learn anything about dealing with these challenges there. You won't even be warned they exist.
I don't think it's particularly a "conspiracy theory", in that there's no cabal of people trying to cover this up. It's more an optimization function; we have N productivity units, and M humans (where M > N), so we hire from the most productive subsets of M. For the less productive subsets (largely youths, criminals, geriatrics), we encourage institutionalization to minimize the portion of M-productive required to maintain the unproductive ones.
If you look at post-industrialization patterns, the age at which humans become productive has been increasing as the productivity of humans has increased. On a subsistence farm, a 6-year old can be doing useful work to increase the productivity of the farm. In a coal mine or factory, an 8-year-old can do productive work. 16-year olds can do construction, food industry, but for jobs with decision-making responsibilities (as more and more jobs are today), we don't trust anyone under 22.
They have? Because last I checked puberty and physical growth tend to peter out around 13-14 for females and 15-16 for males (male growth plates seal at about 15; in females, about a year after menarche, and menses itself stabilizes about two years after menarche).
Does it make his nebulous conspiracy theory more or less believable that you somehow think the age at which we stop warehousing kids actually has nothing at all to do with physical maturation?
Allow me to contextualize all of your controversial deflection:
You specifically selected parts of the body that finish maturing earlier than my statement, because it was the most controversial thing that popped into your head. It didn't pop in to your growth plates, it didn't pop into your elbow. It didn't pop into your left middle toe. It popped into your head.
You should allow these very statements to marinate in that same head, and see if you can come to the correct conclusion as to which part of your body I was referring to in my original comment.