It is so easy for a foreigner to be lied to about her age from a 17 yr.old. 7 Years ago there were fewer heads up than we have today. From a nightmare experience, lucky not to be in the slammer, I strongly suggest, "ASK FOR A LEGAL ID". Apologies for the shout, but sound advice, trust me.
And make sure that legal ID is not a birth certificate, you have no idea of knowing what their real name is. Photo ID is a must (and most don't have one). Don't be fooled though, a fake ID is no defense in Philippine court.