I live in Detroit and come from a car family, all my relatives work for the big 3, most of my bowling league works for the big 3, most my friends and their parents are associated with the industry. This is what they say whenever it comes up.

Vehicle conception to day 1 takes about 6 years, then that generation is manufactured for ~10 years. And the average vehicle lifespan of 15 years (and that is average, meaning that 1/2 last longer)

Since we don't have the tech today, we can confidently say that we will still have a large number of gas powered non-driver-less cars on the road in 35 years from today. Basically cars that get green-lighted in 4 years from now will most likely not be driver-less, then 6 years to develop, then a 10 year generation run, then the 15 year average life of the generation = 2051

I would assume that the following generations will offer driver-less on some (maybe all) models, so they would start conception in about 6 years, then develop for another 6, run for 10.

So we will most likely see the first large scale mass-produced fully driver-less vehicles roll off the line in 12-15 years, But we would still see the majority of generations still standard driving.

The percent of vehicles that will go driver-less is debatable, but the time-frame to day 1 is not. It's been ~6 years since the car was invented. Another thing that isn't debatable is how long they will run a generation, 10 years, why? Because it costs over 1 Billion to develop a new generation and they need to run it that long to make a profit.

So even if the percentage is fast tracked, we are still talking a long time. This current group of vehicles (1) have to end their runs, any generation currently in development (2) or entering development will still be standard, then only a percentage of the following generation (3) will be driver-less, so if the following generations (4+) are mandated to be driver-less, it will still be 15-20 years (lifespan of 3) after the production of that last generation before we will see a society where 99%+ cars are driver-less. Or 55+ years from now or the year 2070.

If the average human lifespan is 78, most of us will never live in that world,

And I didn't even mention the elephant in the room, us, the consumer. What if people simply don't like them and they don't sell? If the first few generation of driver-less don't do well with consumers, auto manufacturers will simply be unable to produce them in great numbers and will scrap future development. Something like that could push it back another 50 years.

Look no further than electric vehicles, we have the tech, and we had if for 30 years and only ~400,000 vehicles in the US are electric. There are 22,000,000 vehicles in the US and only 400,000 are electric. And there is no indication that the next generations are going to be electric save a few niche models. They just don't sell well and a lot of people who drive them don't like them. The best selling vehicle in the US for the last 30 years is a giant ass V8 Ford F150, that is what the market wants and that is what the manufacturers are developing. So as nice as it would be to be 100% electric, it's not going to happen just because the tech is there.

So with driver-less it will come down to the consumers. And if a lot of people simply don't like them for whatever reason, sadly they wont be very available.