I think the biggest difference today is how kids can't easily find places to ride with their friends on the cheap.
When I had my first real bike, a TS50 Gaucho, in 1972 near La Porte, I could push (ride when nobody was looking) to the neighborhood park and ride and explore hundreds of acres of undeveloped land, drainages, and adjoining neighborhoods' fields with my friends on their Hodakas, Maicos, Huskys and Jap bikes.
Nobody interfered. There were no signs prohibiting riding there. I could ride through fields to the gas station and fill up on fifty cents. Today, this would have neighbors calling the law, there would be fines, restrictions, etc. Folks were more tolerant back then and encouraged kids to take a few risks and have fun.
Kids nowadays have to overcome a huge investment in time and logistics just to get to the riding area. The parent has to find time to load up bikes, drive to the special place for dirt riding, pay the entry fees or buy state permits, and more. All these additional factors reduce the time a kid can have on their bike. It is rare that they can just say, "Mom, I'm going riding!" and take the bike from the garage and go ride with the other kids on the block.
This logistical aspect, plus the increasing popularity of four wheelers (and video games), have really cut into the available time and the number of new riders in these younger age groups.
I think that today there are more dirt riders that didn't start riding until they are adults, where in the past we grew up riding dirt with neighbor kids.
Those of us who were in this environment got it into our blood at an early age. It was a formative aspect of our development, and those experiences run deep in our psyche to the point that they are still a vital part of our lives.
I think the opportunity for dirt riding to be this big a part of the life of a youth is rare now, and has been fading consistently over the past several decades.