I finished my degree after returning from an enlistment, and was about 8-10 years older than the typical "college-aged" peer group. Though ages tended to skew older in the ECE department I attended, with at least a quarter of the EE majors being established over-30 professionals and veterans finishing their own degrees.

Variety in age in socialization is a healthy thing, and I feel cramming entire cohorts into a 24-month bloc isn't particularly amenable to how we've evolved.

Your experience isn’t likely common. Most people I went to college with at university were under the age of 25. The overwhelming majority so. I graduated at 23 and was consistently the oldest or tied for oldest in many of my classes. Outside of community college or graduate programs - people age 26+ are very uncommon.

You also spent enlistment time in a similar to college setting for the social aspects anyway, so you would be less impacted by the lack of it in actual college.

This doesn't pass the smell test to me. Plenty of seniors were friends with freshman and sophomores at my university. Maybe it's a bit rare to see an outgoing senior hanging out with a fresh out of high school freshman but less extreme examples were super common.

I just remember that there were some out of military guys in our program and they never really connected with the other under grads. They had more in common with grad students so perhaps they found more friends amongst that group.