> kids primarily only socialize with kids +/- about one year of age

This was a huge realization for me after getting into the "real world". I suddenly had coworkers who had kids as old as I am. At times I felt like I had more in common with their kids than them, because they would mention things that happened before I was even born. I had worked at other jobs before, but excluding the managers, everyone was around my age.

In school, even 5 years seemed like a huge gap--"Wow, he's in college, I'm still in High School!", doesn't seem like that much.