Research

I would suggest turning it around to clearly outline the the specific variable(s) you are interested in. If age of onset is your independent variable, then you need to actually list some dependent variables rather than leaving it open as a blanket statement.... maybe "Does the age of onset for juvenile diabetics have a significant effect on the development of chronic renal failure, visual complications, etc.... by age ___?"

You should always have a good idea of what type of literature is out there, what variables you want to measure, and how you will measure them -- before writing the question. If not, you could find yourself stuck in an endless slog. The key to research is not to cure world hunger all at once. Instead, work with smaller pieces of the problem to gain a better understanding of each step along the way and then put them all together with a model based on the relationships among the variables.