There are still ways to buy yourself into endurance racing, but you'll still need at least one guy on your team who probably came up through karts - that training is just too darned good and there's no substitute for an extra decade or two of wheel-to-wheel competition.
None of my kids were good (or driven) enough to make the step up from city league/YMCA to club soccer at an early age, which means they topped out at middle school JVs.
Oh, and Mario could drive anything with wheels like maybe nobody else but Jimmy Clark, well into an advanced age.
That's not to say he had that much more fun than those of us in the middle of the vintage FF pack.