There are always things people have in common. More-so today with the accessibility to media provided by the internet. That said being a friend to someone isn't about checking a bingo card of similar interests. It's about listening to their experiences and being interested.
What do people watch on tv, what are they listening to, where have they vacationed recently, did you hear about xyz happening in the news.
Kids. People with kids talk about their kids.
Some of that might overlap with your experiences, some of it won't, it doesn't need to. You just need to shoot the shit, hear what they've been up to, say what you've been up to, and enjoy doing it. Maybe do an activity of somekind while your at it, maybe just eat dinner.
The age range is just when people get busy with life and have less free time to actually do things. So they have less to talk about. Work becomes their lives. That changes eventually, wait another five year period. You get settled in your career and your focus shifts more towards what's going on in your actual life.
You should look up 'speech communities'. It's a linguistic anthropology thing. Essentially boils down to 'people talk differently and about different things depending who they're talking to and where'. In your case you want a group of work friends to talk about work topics with, separate from your group of childhood friends, who you can talk about non-work topics with.