I have worked in the same office for 22 years, no one knows my birthday, what my hobbies are or where I live other than "downtown". There is work me and then the real me and never the twain shall meet.
Fair. I do that with most coworkers. I have one maybe two I consider friends and we do stuff outside if work. Those are the people that know me. Everyone else knows the work version of me.
This is sadly very true. Keep most of your coworkers, especially bosses, on a low information diet. It's like dealing with the police. Some of them will try to use anything you say against you in the court of HR.
This is not to say you can't make any friends at work. Just be very careful in who you pick. Make sure the person is trustworthy (and you know as much about them as they know about you).