In reply to kevin stephens:
Frankly I wouldn't bother. I have a full bike license. although I haven't ridden an actual motorbike for years, and have rented 125's on Kalymnos a couple of times.
Last year I was there with my 18yo son who doesn't have a bike license - and never will as long as his mother has any say in the matter - so in fairness to him I also rented a 50.
My conclusion: unless you're riding two up, a fifty is plenty for Kalymnos roads. You can absolutely thrash it to its limits (not that I would, ahem) and it doesn't go fast enough to be scary. A 125 does.