This is one of those topics I feel very strongly about and agree completely with the points in this post.
I struggle to make fandom friends on Tumblr, and sometimes I worry that it is because people in their 20s think they can't be friends with someone in their 40s. That I'm uncool, weird, cringe, intimidating, or just too different from them.
But things don't change as much with age as most think. Older people still are silly, awkward, overwhelmed, enthusiastic, confused, playful, irresponsible, obsessive, dumb, cool, horny, and all these other things young people think we stop feeling or being as we get older. We're just humans. I am really great friends with someone on here more than 20 years younger than me because we have so much in common! You can't tell that we're different ages when we chat.
And also—you can be friends with people who you do NOT have much in common with! Because fundamentally, you always have humanity in common.
Years ago, there was this lady in my community who was maybe 30 years older than me and who I knew was far more conservative than me. I dismissed her as someone I didn't want to spend any time with because she was obviously too different than me. But, I was forced to spend some time with her (long story), and guess what? I became really good friends with her! Because I found out I was wrong about all those things that made her different than me? NO! I was right about that—she was just as annoyingly conservative as I had suspected. BUT that wasn't the whole of her person. She was so much richer than that. There were lots of things I didn't know about her. A few of those things were commonalities, but overall, we still didn't have much in common—but that didn't matter. We could still be kind to each other, help each other, respect each other, even enjoy each other's company if we stuck to topics where we didn't clash too badly. I feel really bad for judging her, and I'm so glad I gave her a chance.
So yes, please make friends with people who are not your same age. You probably have more in common than you think, and even if you don't, that doesn't matter. We're all humans and we need each other. Our communities need us to get along.