snek_boiThe people who believe "progressiveness is just a fad that one grows out of" are the same people that grew up getting brainwashed into regressive politics. The belief is only true for them.
No, there are longitudinal studies on this.
As far as I recall, they tend to show that yes cohorts become more politically conservative but relative to the younger cohorts.
That being said, anecdotally, I do know a lot more people who grew out of communism as we aged (sometimes hilariously so when you look at their careers) than still believe/haven’t tempered it with reality.