I dropped DH, DH's friend and DD off to Leopardstown earlier and there were absolutely massive numbers of older teens and young 20s walking in. When I was a teen none of us had any interest in going to the races. Although we did occasionally go to the nightclub there (I can't remember the name) which was only very young adults and creepy older men from memory.
I'm guessing that there might be some behaviour problems because they stopped selling tickets for teens online and they can only be bought at the door by an adult, possibly to ensure the most of them at least arrive with a responsible adult. DH was going to buy a ticket for DD and DH's friend was going to pose as uncle to DD's two friends to make it look like a family outing. It must have worked as I didn't need to go back to pick up DD.