If You Are Not a Liberal at 25, You Have No Heart. If You Are Not a Conservative at 45 You Have No Brain
This is how I always heard the quote, although I appear wrong
The thing I have noted in my life is that the radicals moderate and move to the center as they age. Black and white issues slip into veils of grey. Hard line positions that paint the enemy as an 'other' crack a bit as you meet more and more people. The exception to this rule is insular communities with minimal interactions with the out groups. This is also why religious and cult leaders are so desperate to keep the flock from being influenced by the outside. Hard to paint people as evil/other when you work and interact with them. There are dozens of ideas I had at 18-20 that came crashing headlong into the wall of adult reality, meeting people who had lived an experience that might have well as been in a movie.
"Maturation" is not the word I think we want to use here. I think that "experience" is a better fit.