For an apples to apples comparison, the 18 year old would generally pay around 75% more than the 30 year old for the same bike. In reality, the difference would be greater if, for example, the 30 year old is married or is a homeowner and the 18 year old is not. In terms of the dollar amount this would generally translate to, it will depend on the age of the bike and the type and amount of coverage desired. On average, for a new Ninja ZX-10R ABS with full coverage, the difference in premium between the 18 year old and the 30 year old might come to around $500 a year, but so many other factors come into play, so this is just a rough estimate. Consulting with your local agent or current insurance provider is a great way to get the specific numbers for your situation.
Motorcycle Product Manager at Progressive