According to US statistics, “overall college enrollment rate of 18- to 24-year-olds (ages in which students traditionally enroll in college) was 38 percent in 2021”.

So if by “most people” you mean, “less than half” then yes you are correct.

Well you can’t make a hiring decision on that basis in most places unless you have a reason. What constitutes “a reason” being variable. Generally if you are prohibited from making a decision on a certain factor, you may not ask about it during an interview.

Sex discrimination can be constituted by various things. For example asking about maritial status, children, plans for pregnancy, soliciting sexual favors, etc. Also in some places, if you thought someone might be trans, you could not ask them about that.

Some of us don’t clutter up our resumes with every job we’ve ever had. My resume lists nothing irrelevant to my current career. I was well into adulthood at that time. Who cares where I went to highschool? It demonstrates respect for the time of the person tasked with reading a stack of resumes to not waste their time.