Frank Rizzo, who was head of the Philadelphia police department from 1967 to 1971 and mayor from 1971 to 1983, was diagnosed with diabetes around age 19 (he served one year in the Navy and was discharged because of his diabetes diagnosis).
I believe he had type 1 diabetes despite the fact that he himself referred to it in public as "mild diabetes" because:
-after his death, his doctor mentioned that he took insulin
-he was diagnosed no older than 20
-it was severe enough a case of diabetes that it was diagnosed in 1939 (when mild cases didn't tend to get diagnosed) and to get him discharged from the navy in a time of war- which would not have been the case if he could have gotten away with controlling it via diet.
If I am correct, then Rizzo lived with type 1 diabetes for just over fifty years; he died in 1991 at the age of 70.
I have, TBH, mostly heard negative things about Rizzo's mayorship- particularly about police brutality and racism. Nonetheless, he was a remarkable figure... and he had diabetes during all of the famous parts of his life.