[maujun]

I believe you are making a big assumption that you would spend a gap year at 18 similarly to a gap year at 22 or older.

A college environment is like a strong wind. Equipment, professors, and students follow and create winds of their own. Those that come in as undergrads will naturally have a different experience than those who come in as PhDs.

After leaving a college environment, a person has changed. In particular, they are better-adapted for interacting with certain types of people, in certain types of (work) environments.