If we waited longer we'd just have a lot of inexperienced slightly older drivers.
Where I live there are restrictions around what new drivers can do, such as driving at night. I think they are largely ignored tbh past the very early stages. They can get a note from their employer to drive at night to work for example but most don't bother, it is too much faff.
I do think that a lot of kids get a licence but not enough practice after that because of lack of cars or especially insurance costs, and that is a problem.
I also think that city driving has become more and more complex and it's a problem for all drivers, but especially inexperienced ones. I'm an experienced city driver, I grew up in te city near me and am there at least once a week. With population growth, adding new bike infrastructure, bus lanes, and more, it's become really complex. Many differernt kinds of intersections, turns, lights, signs, people coming from many directions at once, etc. There are now parts of the city I avoid altogether, and I can't imagine them as a brand new driver.
At my parents' house, to get out of the lane, I now have to cross a double sized pedestrian pavement, a bike lane, and a lane of parked cars, as well as a cement barrier with little metal pylons which seem designed to mess with depth perception, in order to get into the road. A road with frequent busses. And recently freaking electric scooters and bikes which come up really fast, sometimes not in the bike lane. (I am sure one of them is going to get smoked eventually, I know pedestrians are already being hit by them.)
However - I don't think pushing things later is helpful. It will reduce accidents because fewer people will be driving, but that's not a real reduction.