Adult being a friend or family member? I’ve heard about that, and it always struck me as strange, as people aren’t driving instructors, driving instructors are driving instructors.
I think it was somewhere around 6 to 10 hours with a certified instructor. The 40 with an adult was yeah a family member or friend. The quality definitely depended on the adult. My parents took it seriously and made sure we completed the lessons, but I had friends whose parents just signed the form without providing the additional instruction. It was 20 years ago so details are fuzzy.
In California, the first 20hr or so, it had to be a licensed instructor if you were under 18. An adult would just need to register for a learner’s permit and just need any licensed driver in the front passenger seat