We have 2 kids with t1d. Our first was diagnosed at 18 months and old (18 years old now). He was already in dka and spent 3 days in intermediate ICU. Our second diagnosis was 11 years later when my youngest daughter was just shy of her 7th birthday.
We recognized her symptoms VERY early. When we took her to the emergency room and asked the doctor to confirm what we knew in our hearts. He was shocked that she had an elevated a1c and said that he would never asked for an a1c test based on the symptoms that were presenting.
Long story short, she was in the honeymoon phase at some level for about 20 months.