Friendship becomes mature when differences stop requiring defense.

Early in a friendship differences tend to be argued. Politics, religion, how to raise children, what a good life looks like, all become positions to be defended and possibly converted. Later, if the friendship lasts, the differences simply exist and get discussed rather than litigated. That change is what maturity looks like in a relationship, and it takes years and a certain amount of security.

When a disagreement comes up, try asking how they came to think that instead of stating your own view again. Curiosity ends the argument faster than persuasion. It also usually teaches you something.