When are most cases diagnosed? Or is it a fairly even distribution with respect to age?
The mean age at diagnosis is 46, according to this paper published in 2000.
I’m seeing type II DM showing up in 17 and 18 year olds now.
<<sigh>>
One interesting thing is that a lot of the younger folks I am seeing with it (late 20’s, early 30’s) aren’t particularly obese. I suspect a lifetime of high glycemic index foods contributing to pancreatic fatigue and insulin resistance.
I was diagnosed at 32. And yes it was my fault - carrying too much weight, sweet tooth (which is killing trying not to indulge it now), and a family history of diabetes to boot. I was never not going to get it. 
There are also some pretty dramatic ethnic clusters. In EMT school my instructor pointed out that you can almost assume any 40+ hispanic female is diabetic. I don’t know the exact percentages but I know its really common.