Hi Sally. I was diagnosed at age 8 in 1968 and my father and my brother also had type 1 diabetes. My brother was diagnosed at age five, but my dad was aged 27 and they both were diagnosed within six months of each other. I think the reasons for these changes that you described are just because of better detection and much more awareness. If you remember back in those days, there was no internet and I remember my mother going crazy trying to find out information about diabetes from the doctor, who provided very little. All they gave her was a little blue book and that was it!
At that time, my dad was on oral medications and he took something called "DBI." But since he was not doing so well with it, he switched himself over to U40 insulin. And he did this without medical supervision. Back in those days, we were far more independent. But today, with more awareness and education around diet, insulin requirements, blood glucose testing (remember Test Tape?), insulin pumps, pens, etc., the story has become more complex because more people are sharing their stories. I believe that type 1 diagnoses was just as prevalent among adults back then (again, my dad was in his late 20s'), but many did not know it. Whether this can be proven genetically or not, I am not sure, but since natural selection takes time (i.e., "survival of the fittest"), I don't think so. I teach genetics in Physical Anthropology courses and I am up to date on the research, and only future research will tell us if there is a statistical increase in type 1 among adults over the last 50 years. So now, you are not crazy! Hope this helps!