What's the age in the US now? I seem to recall it was at 15 that we could take a one-semester driver's ed class (concluding with a few hours behind the wheel in a car with dual pedals) and take the written test to get the learner's permit, and after our 16th birthday that we could get the full license if we could pass the road test. (Parallel parking was the hard part.) There was no minimum number of practice miles or hours, but since for most of us it was at least a half a year till our birthday, we got enough practice.
Based on what we now know about brains and judgment not being fully developed until around age 21, not to mention the materialism and environmental waste of buying teenagers cars and insurance, that seems too early to me now. But it gives parents more freedom from chauffeuring, which for working parents is not a minor consideration.
Even when practicing with a parent, you don't start in a busy downtown area; the parent drives out to a quiet neighborhood or a country road, or to a big empty parking lot after hours, and then switches places. It's true that those first moments when you're actually in traffic are scary, but they have to come sometime. Our driver's ed class road practice included getting on and off the interstate; I found that much easier than staying under 30 mph in town, or making right turns without popping the curb.
The driver's ed training did help me avoid picking up one bad parental habit. My dad never fastens his seatbelt until he's well down the road, in the middle of traffic; I put mine on before I start the engine, because that's how my driver's ed teacher made me do it.
In rural areas, kids do learn to drive much earlier. We envied classmates who learned at 10 or 12 in a pickup on the farm, and by the age of 14 or 15 had special permits at least to drive to school and back in daylight.