I'm "only" 58 but I don't understand this expectation that 50 years later four guys with four very different life experiences are going to still be the same as they were as kids / young men.

You are very different now, but cherish the time you had together 50 years ago when you were roughly the same. I think that is why you pull out tokens from that time: to enjoy the nostalgia of that time long ago when your lives were mostly in front of you.

My dad didn't have many close friends as an adult. My mom made an astute remark: "You have to be a friend to have friend."

From your post, particularly your last paragraph, it sounds like you don't want to put in the effort to have friends. It sounds like you don't want to accept that 50 years of very different life experiences are going to require you to accept different opinions about major issues if you want to be friends.

You appear to expect that nothing changes people in life, when the only constant in life is change.

Obviously I don't know your old buddies. In my experience, it is shared basic values that are the basis for a lasting friendship. If you guys have that, then I'm betting if you just get curious about what they did all those decades, you can spend the rest of your life hearing interesting stories about their lives.

You can have a wonderful time thinking about how your life might have been if you'd gone the same path as one of them. Ask why they made a certain decision at a specific fork in their lives. That (to me) sounds very interesting. Just listening to people is one of the key factors of being a good friend.