There's no way to force the onset of menstruation; your body will start menstruating when it's ready. And everyone's body is different, so there's no "right" age when you'll start menstruating.
If you're really worried about it, though, why not schedule an appointment with a doctor and get everything checked out?
"The only unnatural sexual act is that which you cannot perform."
-- Alfred Kinsey
[This message has been edited by kythryne (edited 03-13-2002).]