About 13 years. My big tipoff is feeling tired. I'm a night owl and stream on Twitch after a long day of consulting -- I'm NEVER tired before 1 or 2AM.

The most severe problems were the result of a new doctor in their residency changing my long-acting insulin to an intermediate that was also a 30% mix of fast acting, in an attempt to drive my A1C to under 6. This created a serious problem of wanting to give myself insulin for a meal, my blood sugar only being around 90-100 mg/dL, and then being unable to decouple the fast-acting from the intermediate since it was pre-mixed. I hemmed and hawed, but the attending stood by the decision to change to 70/30. I had to change 10 years of regimen instantly, which was fraught with peril.

Two serious episodes later, and a waiting room at a prestigious teaching hospital hearing someone scream, "Your stupid decision has nearly killed me twice", and I'm now back on the long-acting with insulin reactions being rather infrequent (twice a month), and nowhere as severe (catching it around 65-70 mg/dL). My A1C has trended up slightly (6.1-6.2 to 6.3-6.4), but I'd rather that than death by overdose.

Not speaking for the parent, but I'm a 35 year old T1D who has been diagnosed for only about 7 years and I am already nearly asymptomatic when I have low blood sugars. The risk of becoming asymptomatic for low blood sugars increases over time, but it is completely inconsistent. Some diabetics have always been asymptomatic for low blood sugars, others will go their whole lives and always have easy to detect symptoms. I have a friend who is in his mid forties and is also a T1D; he was diagnosed about 30 years ago and he still consistently gets the shakes when he is any lower than 70.

In my experience (Type 1 partner), it's repeated and severe lows, say like 4 or 5 in a week, that will give you hypo-unawareness. It's definitely possible to experience that and still have a high A1C, but I don't see it causing hypo-unawareness. I'd highly recommend a pump to get more control.