The move away from parents starts in junior high, and the young adult doesn't really welcome them back into his fold until about 30. In between he is thrown to the wolves of the youth culture for a workable and satisfying place amongst his fellows who are equally immature by experience and brain function which is incomplete until about 30. In this group acceptance is everything, and being deemed cool or hip is the apogee of that acceptance. No one knows what they mean, and in any case though they would seem to be bestowed by the group, they are really more about an inner certainty that one is superior.
The Beatles were cool. Just look at some of the footage of their early performances, which to mne evidenced a tight musical style played with verve and joy. They were very cool, and they knew it.