Sorry to piss on ya parade....But..
Age 19-20 - 47 bhp max: the A2 licence. This is where the rules become slightly complex. From the age of 19, you are permitted to take an A2 test (which must be taken on a bike of at least 395cc, with a power output of between 25kW/33bhp and 35kW/47bhp). If you don't already hold an A1 licence you will need to do a CBT beforehand, as always, and pass a theory test, before you take the practical test.
Upon passing, the rider is restricted to bikes with a limit of 35kW/47bhp and a power-to-weight ratio of no more than 0.2kW/0.26bhp per kg, for two years. The power-to-weight ratio is an important qualification because it makes drawing a distinction between 'can ride' and 'can't ride' more nuanced than a simple bhp cap. In real terms, it imposes a minimum weight of 175kg for any bike using the full 47bhp, dashing hopes of super-lightweight 250s making a mockery of the bhp limit.
It's relatively straightforward to restrict a bike, meaning you are not necessarily ruled out of riding the bike of your dreams - unless you are dreaming of anything 'more than twice' as powerful. Any bike originally making more than 94bhp is still out of reach of the A2 licence.
You will need to hold the A2 licence for two years before you can move on to a full A licence.
Age 21-23 - you must be 21 to hold a full, unrestricted A licence. However, at this age you can only take the test if you have held an A2 licence for two years or more. It is important to note that unlike the current system, you are not automatically upgraded to an A licence without a further test. If you started riding after 19, and are not yet 24, you will be restricted to A2 for two years regardless
God bless the illegal state that is the European Union