I've kind of questioned a few too. There are some that claim to be in their thirties but act like prepubescent tweens, and there was someone on here who claimed to be in their late sixties but acted like an adolescent or young adult.
Everyone does it for their own reasons. I'm actually 12, but want to avoid the annoyance of hyperactive little motormouths with pimples and braces constantly bombarding me with photo's of their underdeveloped breasts. I figured if I said I was 60 I'd be safe, and it's worked out brilliantly!
I'm immature plus I look 15 so that blows really hard because I can definitely be mistaken for one :( I do not show my immaturity in public unless someone is the same, they definitely have the ability to see through my façade... hell one girl managed to see through it xD
Yes, some people do choose the wrong ages. However some people are very un-experienced for their ages. Usually people have a age in mind , where they expect a certain experience level, but those who were sheltered, anti-social, career focused will not have the same experience as someone who mixes around crowds, goes out all of the time, and maintains a very actively social life. I've been able to advise those double my age on certain issues one would "expect" them to know. Age doesn't necessarily define ones experience level.