There is one thing that doesn't change as you get older: you have to keep making friends as you go along. I don't care how old you are or how many good friends you've already acquired. Life changes too much to expect to be around those same friends and for them to be available to meet you at your current life's situation at any given time. Sure, we should pour into our past friendships and make attempts at not letting them die out. But someday your friends will literally die, or at least not be as available to you as they once were. What will you do then?
I work with an older man. He's almost ready to retire, but he is still working as a lawyer, so I help him out as a large part of my job. He is a very interesting man, but I'm starting to realize part of what makes him so interesting is that he is so interested in other people. He considers me and my husband his friends, because he often asks how we are doing or wanting to know if we want to do something else with him. He has so many stories to tell, because he has been this way his entire life. He meets a person, and wants to know about them. He wants to be their friend, regardless of how many friends he already has or age dynamics.
It is smart to continue to be seeking out friends, even to the very end of your life here on earth. If one thing is certain that comes with aging, it is that many of your loved ones will die. I have had older people be very candid with me that the reality is that your pool of friends just inevitably shrinks as the years go. Our fallen world sees to that. Don't be the type of person that finds themselves always unhappy in new places or situations because you don't have your good old buddies from high school or college beside you. See it as your duty to seek people out continually. When you are always interested in getting to know people and do things with them, you are making investments in your own future, as well as theirs. You are widening your world view, and you're battling future loneliness.