OK, I'll have a stab at answering your questions here, goes.
1,2 and 3 I don't see a way that you could enforce this as it would require police to pull over and check almost every car carrying 1 or more passengers unless it clearly visible that the driver met those ages.
New cars can detect speed limits. this is strictly true is it? Do you know for a fact that all new cars can do this? Then you also have the fact that a speed sign could be obscured by say a bus, lorry, overhanging tree etc or even be defaced enough that system cannot detect the limit. You mention that they can also know the limits from Google maps, but someone has to update Google maps with the latest speed limits, which have recently changed in Wales, do you know, if all these changes have yet been updated on Google, or even TomTom and other sat navs. The built-in one in most Skodas and other VAG cars for instance will not know that info either. I have just updated to the latest maps on mine, and there are speed limits shown on it which do not reflect those in my city for instance.
Apart from that how many teenagers do you know could afford to buy a new car with the latest tech, let also get insurance for a new car?
The US rule of no passing of buses when they are alighting passengers, given that most buses the days are front entrance ones, you are unlikely to know if the bus is stopped at a bus stop for passengers to alight or disembark, or if it is just sitting in a traffic jam.
To my mind, there is only one way to attempt to cure the problem and that is far better training in the first instance and far more police on the roads in unmarked cars so they can observe a person driving and if required stop them and deal with any observed problem before a nasty accident occurs, and it is too late. Speed cameras are not the answer, only more police on the roads, both high visibility and low key can do this.