--they certainly could order a longer glucose tolerance with several more draws and with insulin levels concurrently measured, which I think might provide more insight.

I suspect he is borderline. The A1c test is useful in that it provides an average of glycated hemoglobin over an eight-to-twelve week period, but one does not know if these averages come from a relatively uniform level of glucose in the bloodstream or from significant peaks coupled with significant lows. The longer glucose tolerance test with concurrent insulin levels is better at seeing this--one can see how one's insulin levels are at baseline, how they respond to the glucose ingestion, and how long the cycles are.

A fairly common finding as people get older is fairly "normal" glucose levels to start, but somewhat elevated insulin levels needed to keep those glucose levels, and an overproduction of insulin upon challenge to keep glucose levels out of diabetic ranges. Sometimes the glucose spike is so big that a reactive hypoglycemia occurs in the second/third/fourth hour. This is often referred to as "insulin resistance" and indicates difficulty getting glucose into the cells; this is often a harbinger of future diabetes. Muscle building is often a way to combat this--muscle on the whole is less difficult for insulin to drive glucose into. (And, of course, losing fat helps.)