It's harder to make friends when you're older because you're less likely to have the 3 conditions needed...

... conditions that were so much more likely to be there when you were in college:
proximity; repeated, unplanned interactions; and a setting that encourages people to let their guard down and confide in each other."

Maybe you can get all 3 at work, but if you think you have that third one, you might be setting yourself up for a backstabbing.