Your main chunk of insurance cost will be in your first year. Once you reach the 1 year point, rates will drop like a bomb, at least, in terms of full coverage. Get some online quotes for a better feel of cost as there are many, many variables that decide your premium.
As for age and mileage, I have had my 2010 250 since 2/10 with almost 40k miles, and she performed magnificently on the 4k mile trip I just return from. She'll be going for at least another 10k, and if/when the engine dies, I'll buy a new engine (instead of new bike). I may buy a second, bigger bike, but I will never get rid of my Carla.