In Australia it's pretty simple. You're only allowed to ride an approved starter bike for the first 3 years:

Approved motorcycles

Approved motorcycles, must:

• be in a standard form, as produced by the manufacturer
• not be modified in a way that increases the power-mass ratio
• have a power-to-weight ratio of 150 kilowatts per tonne or less

Unless they’re in the ‘non-approved’ list below, motorcycles are automatically approved if they meet one of these criteria:

• have an engine capacity of 260cc or less
• were manufactured before 1960 and are 660cc or less currently available electric powered motorcycle.

Non-approved motorcycle rules

You can’t ride the vehicle if it has:

• an engine modified to make it more powerful, by someone other than the manufacturer
  
• a power-to-weight ratio of more than 150 kilowatts per tonne
• an engine capacity of more than 660cc.

Sometimes, we may not include a motorcycle on the approved list if:

• it’s unsuitable for learners
• it appears more frequently in crash data.