Geektastic:
It relates to this, I suspect:
"If a rider passes their motorcycle test (A1) at 17 years old they are restricted to a 125cc motorcycle producing no more than 11kW (14.8bhp) for two years.
At 19 years of age a rider who has been riding on a full A1 licence for two years can take a further practical test on a motorcycle of at least 395cc producing between 25kW (33.5bhp) and 35kW (46.9bhp). On passing this test, the rider can ride a motorcycle in category A2.
Two years after passing the A2 test a rider (21 years and over) can take a further test on a motorcycle of at least 495cc and producing at least 40kW (53.6bhp). Following successful completion of this test the rider can ride a motorcycle of any capacity."
Edit: that's the UK rule which is in accordance with EU rules.
I guess that's safer, but expensive if you have to keep upgrading a bike, or don't want to buy rusty dungers to get you through these levels. IMO if you can show in a test that you have full control and capability of the 50cc or 750cc bike that should be enough


