Have you done other types of yoga before? I'm 66, have been practicing yoga for the past 16 years (mostly kripalu style)and I wouldn't even dream of taking bikram. Older people typically have trouble with the body's temperature regulating mechanism, and even if it's only a very slight problem, bikram yoga could be seriously dangerous.
Also, yes you can go hypo in yoga. I'm also thinking it might be more difficult to tell when your body is so overheated whether it's a hypo or whether it's a blood pressure problem or an increase in body temperature problem.
There are other types of yoga that are probably more appropriate for those of us who are older and also diabetic. The class I took for 15 years was a very gentle one using the kripalu philosophy, which emphasized being kind to one's body and not overdoing. I still practice on my own at least once a week.