Why can’t some adults act their age?

I think there’s a difference between debating or having a conversation with different views and just flat out arguing. Some people can’t handle certain conversations especially controversial ones. Personally I’m the type of person that can respectfully disagree with your opinion without taking offense or trying to shove my opinions down your throat. If I don’t like a topic or conversation I simply go on about my life and move on. Some people just can’t. They have to have the last word or something. That’s life I guess