30 now and still got my old friends (group of 5 or 6 of us) who I go away with once a year. But due to work, family, drifting apart, etc we only see each once every 3 months now. Don't really have that many work collegues as they all live quite a distance away and the gym I go to is pretty anti social.
When I was at uni or school always seemed easy to make new friends. Now I haven't got the foggiest how you make new friend's or meet new people outside of the workplace as a grown adult.
I'm lucky in that I have a girlfriend of 8 years who I count as my best friend but tired of weekends stuck in with just my girlfriend be nice to go the pub or a bar with some lads and have a laugh which I can't do with my old mates no more.
So yeah how hard is it to make new friends in adulthood and how?
For most people it doesn't get much easier. You're stuck seeing the same douchebags that you probably have nothing in common with at work for 8-12 hours a day, want to go home to a hot meal on the table, do butt-stuff with your girlfriend and go to bed. When you're in school you're meeting new people constantly, building a circle of friends, and generally spending a much larger portion of your time having fun than you are working.
Surely there has to be a sportsbar somewhere where you can go, grab a pint and look for someone to talk to? Maybe there's nobody alone, but a group of 2-3 dudes that's easier approachable than a huge gang. If not, take your girl to a pub with some pool tables, buy some drinks and grab a table -- maybe there's another couple there that you can challenge to a friendly game.
Outside of meeting people at bars it sort of comes down to your interests. You or your girlfriend like to cook? Find a cooking class and the two of you sign up. That sort of thing. Keep trying at your gym - it can be awkward to approach people because gyms in general I have found to be a place where people aren't necessarily looking to meet new people. People go alone or with a workout buddy, do their thing and go home. I work out with a friend, but the reality is I'm not an asshole (and neither are most people). If somebody came up to me and said "I'm looking for somebody to work out with" I wouldn't tell them to fuck off. I'd tell them what days/time I'm usually at the gym and welcome him to join us if he sees us around. If he didn't turn out to be a total weirdo we'd probably grab a beer/hang with outside the gym at some point. So while neither of us are necessarily approaching other people for the intention of making friends, if somebody came up to us we'd be cool about it. I'm lucky that I have a good friend who I work out with after work, and then we go to one of our places and make dinner. Borderline bro-gay, but both of us are single and we like getting high after working out and cooking.
The reality is though, that around the 25-30 age life slows down for nearly everybody. You and all your friends from college have probably scattered across the country or the world for work and you rarely see each other -- I'm in the same boat and also 30. Unless you're lucky enough to constantly travel or meet new people through work you've replaced the largest portion of your day (school - easy to meet people) with work (hard to meet people).
The thing is -- if you're afraid to approach somebody at your gym, or a group of people in a bar, the chances meeting somebody become pretty thin. If you want to meet a new beer-buddy / start a bro-mance you sorta need to throw yourself out there -- it's kinda like dating. What's the worst they say -- leave me alone you friendless weirdo?\
I met my workout friend through a mutual acquaintance. One night I was with the mutual acquaintance, and he got a phone call. Future workout-friend just bought his first house and was looking for some help to move. Bored, we agreed, and moved a bunch of shit with him. We got high and chilled for a bit, he thanked us, and said we should grab a beer sometime and gave me his number. A few weeks later I was bored, texted him and asked if he'd be interested in grabbing those beers. He said sure, and we've been best friends for 6 years now. I been on countless fishing trips with him, we've gone to Jamaica with other friends -- if we were gay we'd be a couple. At the time I thought it was gay/stupid to ask this guy I knew for maybe 2 hours out for beers, but if I didn't send that text I would have never gone on all those trips.