This is just anecdotal experience but most people I know even now that are die hard football fans only really got into it when they got into college age, including myself. I was as nuts about Pokemon, GTA, Harry Potter and skateboarding as any kid out there and couldn't care less about televised sports, but kids tastes change pretty dramatically once they get through puberty. And if they don't the NFL/NBA will have years to adapt to an internet and highlight focused model. You only have to look at the sea of adolescent rocking the Mahomes haircut to see the effect the NFL has on kids.