I graduated from high school a year early, went immediately to community college to start summer semester, and immediately from community college to a "commuter school" to finish my degree. No problems, no worries, my grade point average actually improved at each step. After graduation, I spent the next seven months job-hunting and working as a forms clerk, still living at home.

Then I went to live in a dorm for one semester of grad school. That's when it hit the fan for me--at 21 when I left home, not at 16 when I started college.

So I think it's more a "first time away from home" thing than it is a "straight into college" thing. It's just that for many people, the two are synonymous.

(A few years later, I did go back to school part-time and get my master's degree, largely because I needed to prove to myself I could do it. Things went much better the second time around.)