Is it possible to select all events in my city where most attendees are within my age range?
Using facebook graph API, is it possible to make a search that would return a list of all events in my city, where most (say >50%) of the attendees are within my age range (say born between 1995-2000?)
No, you can't!
What you could do is, fetch all the events in the city, do a loop and check the data you need. I haven't tried to fetch attendees information but i think it is impossible until the user has approved your app.
But @luschn was wrong here. You actually can search events by city. With a simple graph api search like this: search?q=cityname&type=event
But keep in mind that not all the events are displayed there. You could also do what @luschn recommended but it will take a lot of time to go through all the pages and their events.
If you're trying to build an app that would show nearest events then it's pointless. Theres one website (https://www.minek.ee/tartu). It's in my mother tongue but you can use the search to search events outside of Estonia. I bet that this website uses the same tactic to fetch the events but they are doing the fetching in background while displaying you all the fetched events one by one.
Still, this app doesn't have much traffic so i think there's no point to build anything like this because people really aren't interested in this. I know that i shouldn't give out opinions but i'm pretty sure that building this is just waste of time. Why?? Because i've already built one and it wasn't worth the time.