That's the age range it replaces X with. It conducts the query multiple times, across that range. It makes sense if you just press "Go" when you visit the page

That's the age range it replaces X with. It conducts the query multiple times, across that range. It makes sense if you just press "Go" when you visit the page (don't change anything). My first instinct was to replace X with an integer and you only get one result when you do that.