It's definitely harder to make friends when you're older outside of work acquaintances (at least I've found it true, YMMV). I'm an introvert, friendly but in no wise would I be called outgoing, and I'm not much of a joiner. These traits are not conducive to making lots of friends. Finding friends is important, but so is connecting with peers. What I really find depressing is the lack of intellectually stimulating conversation at work.

While I'm now in a local job, the department I'm attached to is in a satellite building far enough off campus to make it impossible to just meet up with my peers. My co-workers are nice, but they're not really colleagues or peers in terms of my professional development. I'm a technical person in a functional/business analyst role where I support a group of non-technical users. I almost never have the opportunity to discuss implementation details with the developers and I rarely meet with other analysts face-to-face. Online interactions will have to scratch that itch, for now at least. Though I do fear with the spread of the 'gig' economy, the ease of outsourcing, and increasing availability of remote work, this loneliness is only going to be a growing problem.