[matchbok]

That's not what the previous poster said. They were talking about socializing with people your own age, which is critically important. When I was 18 if I acted like a 40 year old I would have never made friends or found a girlfriend.

[lmm]

But relative age is not what makes the difference. Interacting with 20 year olds as a 20 year old is much more like interacting with 20 year olds as a 10 year old than it is like interacting with 10 year olds as a 10 year old.

[EdwardDiego]

Depends. Will you know the slang your 20 year old peers use if your main source of socialization is 30 year olds? Did you go through all the same cultural crazes and fads?

A shared culture is important, and each generation has their own touchstones.