Unsure about overseas licences
Basicly this is how our tests go
16 years old restricted to 50cc
50cc and under you need a provisional licence and a cbt(compulsory basic training)
17 years old you can ride a 125 and under licence Same as above
Anything above 125 needs a full bike licence
21 years and under you can take your full licence but are restricted for 2 years to 33BHP
if your over 21 you can take a direct access test which enables you to ride any bike
Before you can even start training you first need the CBT then you can ride something over 125cc under instruction then you need to take a Theory Test Then you can take the main test.
If your coming over from the US make sure you have VALID insurance. The uk have stiff laws about this. No insurance your bike is instantly seized and costs around £120 to get back plus £10-£20 each day its left in the compound. After 7 days it is Destroyed
. It also will not be released without someone with a valid licence and insurance to take it away.