Ditto to >...Missbehave...< and ~Rebecca. But please, even though he/she probably SPAMs a lot, there's no need to treat him/her like an outcast or being mean to that person. They're still a person, no matter what.
But still, please don't go around SPAMming; things like that make your karma bad.
Anyway, on-topic...
Computers can't actually tell that you're lying, although a polygraph can. A polygraph is the scientific name of the lie detector.
A lot of people fake their age online. That's where online predators come in. They go and fake their age just to get some girl to spill her name, address, phone number, etc. That's why I just avoid taking ages too seriously.