I’ve heard figures like 10 years of lost life expectancy, but I assume that is a mix of people who have the issue under control and those who do not.
So if you have type II diabetes and are diagnosed in your 40s or 50s, what is your life expectancy and disability rate assuming you manage to keep your blood glucose and a1c either in the acceptable range or the mild diabetes range (I assume mild diabetes range means an a1c of 8% or less)
Here is a relatively recent article that reaffirms the “about 10 years off life expectancy” for people with diabetes over age 50. A bit of good news - it states that it’s more like a loss of 8 years on average (see 1st paragraph of ‘introduction’).
The more important reason for citing this paper is that it is full of great references regarding your question(e.g. refs #4 thru #9). The best news is in the article’s reference #9 (available here with free full text), which claims a normal life expectancy for at least some people with type II diabetes if contemporary medical management is employed (particularly regarding things independent of the glucose level such as blood pressure and cholesterol control, anti-platelet drugs (“blood thinners”), etc. I think you may find the “Discussion” section of this paper especially informative and accessible.
I must be honest, though. As much as I would like to believe people with diabetes can have a normal life expectancy, that is still more of an aspiration than a reality, notwithstanding the paper cited in the previous paragraph. The results in this article (free, full text) are more typical. I am sure you will find the tables and figures of interest (not to mention the next).