I realise that you're not going to change your generally safety angled point of view Stuart, but as said, it's not what I'm arguing. It's this simple logic:
Here is a law that bans those under 14 from riding something classed as a bicycle, when the law says that they can ride something classed as a bicycle.
Your contention that electric bikes are motor vehicles is wrong in law, both here and in Europe, they are just bicycles. If the legislators wish to class them differently, they have the option to argue that case, but they have not done so, so the age limit as a nonsense.
Meanwhile, they are certainly not similar to motor cycles as you say, they are almost entirely normal bikes which have some provision to help with pedalling. By extension, what you say means that the few kids who ride fast lightweight thin tyred sports bikes should also be banned. After all, their bikes also make pedalling very much easier than that with the usual kids bikes, and they are capable of higher speed than any legal electric bikes.
The safety issues you raise remain irrelevant as I've already pointed out. Take riding on the pavement as one example. As you say, they already do that, and an electric bike would not allow them to do it any faster than they do at present. The fat tyred dual suspension all steel bikes they commonly ride weigh at least as much as any of my three electrics, so weight is not a factor. They have the same braking abilities. Therefore the ban has no function, there or for the other issues you raise in each answer. Ergo, what is the point of this law?
It's rare for such a prejudicial and pointless law to get onto the statute books, and to prevent these we have select committees and the house debating chamber where such proposed laws can be challenged. In this case though, those affected are without representation in our democratic system. The age limit has clearly been included by those like yourself who have childrens safety in mind, but it just as clearly hasn't been thought through, it's just been included as a knee jerk reaction. If it had been thought through, it would have been abundantly clear that it could have no effect or purpose.
P.S. I didn't answer the point you previously made about chipping to make bikes go faster. I think you've missed the point I was making Stuart. Most of these cheaper bikes don't have any electronic limitation, they only have enough power to reach 15 mph or a bit less on the flat. No amount of chipping can alter that, there's no more the motor can give. Bikes like some of the eZee models are the exception and reside in the upper price bracket which parents won't be entertaining.