They have a regular police presence due to historical problems. Not quite an officer stationed there, but pretty close at certain times of day. Helps that there is a police substation next door. Calling wouldn't get an officer there any quicker, when one walks thru or past every ten minutes or so anyway.

There is a big cultural, uh, mismatch where the library requires more police intervention than any of the retail stores or bars or parks... liquor licenses have been lost for consuming far less police budget than the library. The library gets a free pass.

If all the policies were printed out from the web page it would be at least 100 printed pages. It is a very verbose CYA that boils down to anything you do that a librarian doesn't like will get you banned, and being there while banned is a legal trespassing offense, so one strike and you're out. If the librarians like you, you won't be banned no matter what you do. I can photocopy copyrighted materials, take pictures or videos of my kids, talk (whisper) on my phone, hang out for an hour while my kids take a class ... folks of a different race or economic group may have a somewhat different experience when they break any of those rules.

I was unable to find a minimum age, but I think you'd have to be at least upper grade school to survive not violating at least one of the hundreds of rules for more than a minute or two.

I did find that they define loitering as being in an area for longer than 15 minutes other than defined study desks, so no need for crayons or tagging. I've violated that rule a few dozen times, but I'm in no danger of being punished...

Given the sheer workload of homeless people and child day care, the librarians show quite a bit of restraint and can't enforce all the rules.