My work is almost exclusively filled with 20 year olds, I'm only 29 myself.
I also coach wrestling for Youth & Adults, as well as compete in Jiu Jitsu.
I was an Uber driver for 2 years, a medical transport driver for 3 years, and worked with 16-24 year olds for 3 years at a trade school.
Between all of those gigs, I have barely ever known any hardcore boxing fans. Lots of people tune in for the big May vs Pac or Canelo vs GGG, but don't follow it. Conversely, I've met tons of people who follow the UFC in those gigs.
I think the UFC has been bigger than boxing in America for a very long time now. The biggest boxing event will draw in more people than the big UFC event, but there are way more people in America that follow the UFC than people that follow boxing.