As a 'young' driver I find this completely stupid. Although i do belive at least one manadtory 'night time' lesson while learning, it is completely different to driving during the day.
As for a limit on the engine size? Also daft imo. I first tried to learn in a 1.2 astra when i was 18 and i hated it. I felt it was sluggish to respond, under powered, and very frustrating when you press down on the accelerator and it take a good few seconds for it to kick in.
After that I got some lessons in a 2.2 turbo Accord and a 1.9 Ibiza. Much better response, and much more comfertable and so i felt more relaxed and confident in my driving. Just because a person prefers a bigger engine does not mean its all about the speed. There is a lot more to consider!
Everyone has to learn, and banning an age group from somthing is only going to make things worse.
Oh, and I also passed first time, had no crashes or accidents, and I drive at all times of the day, and in most condisions (snow included!) unless it is complelty dreadfull outside!