I generally make myself significantly younger than I am, because I fear it will send me to a page informing me that 'you're too old to be playing video games, grow up man!'
I guess its about legally coveirng themselves. Its a bit like the way immigration forms to the US always ask if you are a terrorist or if you commited war crimes in Europe during the 1940's. Many stand-up comics have observed that nobody is going to say 'yes', but I'm guessing that by making the guilty lie it makes it technically easier to deport them later if it turns out they are Martin Boorman or something?
IT IS REQUIRED... even tho most of the time people lie on them.
But if something should happen, the company can say YOU LIED about your age and parents are at fault for not enforcing their children and internet activities, when some anti game activist yells its not suitable for minors to view.