No one will be convinced by "grow up" (as I was myself unsuccessfully told in different ways at different times), but the trend of conservatism increasing with age is true.
I knew the trend and took steps to resist it, but now I understand what undergirds it and why it is positive and to be embraced:
First, a sense of responsibility can increase with age.
This can crudely be reduced to having an accumulation of things and wanting to preserve those things and as such dismissed as contemptible.
That dismissal is itself contemptible (if perhaps excusable in the young).
It is not "Marxist" in that Marx's point was precisely that "things" are important to expanding the powers of life.
Most importantly, on a human level, it undermines the very kind of solidary that Marxism--if it were to work--would require.
I resisted having things to lose to resist the trend, but thankfully I could at least care about other people having things to lose (more on how Syria in particular changed my thinking later). As such, I had a basis to rethink my theory when it conflicted with reality, even if it took decades to happen.
Second, only with the accumulation of knowledge can come a decent grasp of history.
History is one of the domains most improved with accumulated knowledge.
Math and physics breakthroughs come from relatively young wunderkinds. Historical insights do not.
Related to a growing sense of responsibility, a growing awareness of the vissicitudes of history strengthens one's sense of the trade-offs, compromises, and twists and turns as compared to a Manichean flattening of the world to pure and impure, good and evil.
This is, of course, worsened by an education system that is designed not to educate.
Contrary to the progressive idea that this is explained by the education system's roots in industrialization, to a large extent it is due to the influence of 'progressive' ideas (like the now infamous attack on phonics--which, wistfully, might lead to a reevaluation of other such ideas, like the attack on memorization or having to learn things like history rigorously).
In relationship to Marxism in particular, while I was educated in Mississippi and the leftist idea is that educational institutions are dominated by conservative ideas, the truth is I was not forced to confront the reality of Soviet totalitarianism in my education.
The United States ended the rule of Soviet totalitarianism, initiating one of the largest and most significant expansions of freedom in history, yet the historical memory of that is not preserved and nurtured (contrary to Chomsky's ideas of American empire and propaganda).
Increasing conservatism with age is not antithetical to the desire to improve the world. Rather, it can help one develop a more nuanced and compassionate worldview, that can recognize the value of both individual responsibility and collective solidarity in working for a better future.