Great news, this isn’t actually true!
Okay, well, the number of people alive the exact same number of years as you is gonna go down. But that number is arbitrary and doesn’t matter.
The thing is as you get older the difference between you and people younger/older than you gets smaller and smaller. You’ve probably noticed that as you get older you can form relationships more easily with people even years older/younger than yourself.
As you get older, more potential friendships and relationships open up to you, until you’re well into old age.