You captured two of the author's points well: 1) more vulnerable, intimate conversations that eschew social norms can lead to more and deeper friendships; and 2) to grow deeper connections you should cast a wide net and filter down based upon compatibility. The author makes other points about taking initiative and following up as well.
Your critique of point #2 is that a middle-aged adult has less opportunities for casual conversations with a stranger than a university student?
Maybe. Off the top of my head, here's a list of places a middle-aged adult can find casual conversations that may lead to friendships: gym, grocery shopping, volunteer work, hikes, walking in the park, sports, library, cafe, public events, bar, club, mall, in the checkout line at any store... I can go on. If you consider all these different avenues, you encounter 100+ strangers every day.
I'm a middle-aged adult that had no problem making friends throughout school. It was easy, almost the default. I lost most of them to time and distance. And now, I find myself with little to no close friends, outside of my family and significant other, because making friends isn't the default as an adult. Making friends takes work!
The author correctly highlights that you must exercise intent to make friends. I've discovered some parts of this through trial-and-error over the past couple months as I've been intentionally putting myself out there, and have received promising results so far. I still have a ways to go.
I leave you with a recent experience of mine that touches upon a lot of the author's points.
I workout 5-6 days a week at the gym. Headphones in, don't bother me. I see this same guy every day I'm there. He's working out, but he's talking with people too. Half the people there know him. For weeks, we'd pass by each other and say nothing. Until one day, I passed him in the hallway and asked him "How often do you work out and for how long?" Such a random question, but I was curious because I see him every time I'm there no matter the time. He gave me a long detailed rundown, told me about his 165-day streak, why he does it, etc etc. We exchanged names and then went about our days. Since then, we've spoken to each other every time we see each other, and our conversations have gradually gone deeper and deeper. And there's something strange about him... he's present. He's not in a rush, he's fully engaged in the conversation, and he's not afraid to talk about anything. So when we talked about what we did for Thanksgiving, I shared a little bit of vulnerability about how most of my family and friends are spread out across the country in different locations. Well, he was familiar with one of them, and actually traveled there to propose and get engaged. Turns out we'd been to some of the same places off the beaten path and enjoy the same things. Then the next time we talked, I asked about his wedding, and he shared some vulnerability about how the woman left a year after the engagement, just before the wedding, so on and so on.
This experience isn't unique. Since becoming intentional, open, and willing to share my actual self, I've had this same experience many times over the past couple months. Once with the cashier who was checking me out at a sporting goods store. Our conversation twisted and turned into her sharing vulnerability about growing older, with her birthday just a week away. Now, when I see her, we have real meaningful conversations without feeling like we have to be "normal".
Yet still, after these positive experiences, I don't exchange information, follow up, or take initiative. And that's what I need to improve upon. Because why wouldn't I do that after having a few good conversations? Well because I'm scared, I don't want to feel like I'm imposing, and what happens if we don't actually get along. Oh well... just have to dive in. :)