I can't speak on how social media is supposed to be used (since I don't even have a facebook account), but wouldn't the kid mostly be in contact with people who

I can't speak on how social media is supposed to be used (since I don't even have a facebook account), but wouldn't the kid mostly be in contact with people who know him or her outside of the computer (such as friends and family), making the "displayed age" (you can turn the display off, right?) useless? Faking a birthday seems pretty harmless and I don't see how it would hinder your experience on anything unless you enter the wrong age that gets you banned like this instance. When I was in my early teens I role played on a game and met a lot of people there I'm still in contact with, I interacted with 20+ year olds when I was 13 and there were a few younger people too. Of course, I didn't fake my interests/gender/etc. but I've never been in the habit of storing age/location info with a private service; it's available publicly anyway, but you have to use inductive reasoning to link the data. If you want people to know your birthday, I don't see why you can't just tell them in person or email or whatever and leave the "official" fake birthday what it is.