I'm also in my 30s, in Denver and struggling with the same problem. I moved to Denver 2 months ago and realized something rather painful - I haven't actually made new friends in over a decade. It's always been difficult and I've been comfortable with a few folks I am close with. The problem is now they're not here and I just can't seem to take the next step with people I meet and move past the acquaintances stage. Anyway, if you'd like to meet sometime for coffee or something let me know. I'd be happy to chat :)