Certainly there seems to be more type 1’s at an older age, but also just in general. Maybe it’s a predominate gene getting inherited more, maybe the viruses that set it off are around more who knows yet? But a lot of it in the past is the misdiagnosis’s of type 1’s that is still currently an ongoing problem.
It used to be presumed type 1’s got it mostly as kids, it was referred to as juvenile diabetes. The prevailing theory is that type 1’s that got it when they were older in the past were misdiagnosed as type 2’s. You are more likely to get type 2 the older you get. And it still happens a lot. 50% of type 1’s are over the age of 30, and 35% or more are still misdiagnosed as type 2’s at first. But it's also why they refer to it as type 1 now instead of juvenile diabetes just because of the acknowledgement that all ages could get it. And a lot of the medical field is still behind. I've run across a couple of doctors that still automatically think I got it as a kid. Our emergency room recently sent someone home that even asked if they could be a type 1 and was told he was too old, he was in his late twenties. He got a call the next day to get back there, the tests came back saying he was a type 1.
They think that an overworked pancreas can wear out over time. And that is what you were taught years ago would happen to a type 2. It turns out that less than 5% of type 2’s are insulin deficient to some extent. But type 2’s when nothing else works are put on insulin, so if you were a type 1, it is also what you needed. And in adults since the process happens slower, meds and lifestyle changes work at first because you still make some insulin, helping to mask you are actually a type 1. It doesn't suddenly stop usually as an adult, and the odds were, you would have been put on insulin by the time it does, because nothing else was working anymore. C- peptide and especially antibody tests are relatively newer. C-peptide was first discovered in the 70's and GAD in the 90's in reference to diabetes. But I bet not widely used yet for quite a few years, And still isn't in a lot of countries because of costs.
Misdiagnosis is and was a huge problem. I know because I was misdiagnosed for over 8 years. I asked if I could be a type 1 because I had an uncle that was a type 1. I ate healthy, swam 75 laps every day. Type 2 didn't make sense to me and I kept getting worse. I was told no and they never tested me, I believe because I was overweight and 46, they just assumed I was a type 2. I switched doctors, who sent me to a new endo who tested me right away and I was finally diagnosed right. If I had stayed with those doctors would I ever had been properly diagnosed? 8 years was a long time and I was on insulin so I was surviving. There are many many around with similar stories.