Id like a motorbike some day,but im 19 and so the limit is 125 cc
im not looking forward to going though all the tests so i keep putting it off,and i cant afford a bike at the moment anyway so by the time i do get one the 125 limit will be lifted
But that limit's only until you pass your test, then you can go to a bike upto 33 bhp. There are plenty of restricted bikes available in this category.
After 2 years on that you are unlimited and can ride what you want. It's only CBT followed by one test tho, and you can pass it all in a few days on a course.