--absolutely rise with age for most of us; in fact, there has recently been a spate of articles, including one from the New York Times, about how this needs to be recognized more so that "prediabetes"--the level you're just edging into, according to most lab ranges--is not overtreated:

How Meaningful Is Prediabetes for Older Adults? - The New York Times

In my estimation, you're doing pretty well if you're 82 and this is the first time you've edged up to an A1C level of 5.7. And there are always dietary adjustments one can make, but probably the best defense of all is to try to do some weight-bearing exercise, if you can, to build a bit of muscle mass (which can be done at any age); muscle tends to process insulin better than other tissue types and helps with glycemic control.