If you were old enough to grasp how 9/11 changed the world as we know it and have clear memories from that day, you’re a millennial. If you had to be taught about it then you’re not.
Everyone has their own definition but that’s always been the cutoff that’s stuck with me.
The headliner refers to the main entertainer of the the show that comes on stage after the opening/warm-up acts finish performing. You have to get through the opening acts before you see the one you actually came for.