I love Garmin metrics. It's an ecosystem, expensive, but the numbers rock.

I am sure this has been covered already by the volume of replies, but approximate max heart rate is computed by age. It appears that Connect has done the same, based on the zones it shows. (I am at the upper end of my 40's and my theoretical max is ~188, I believe.) For Connect, I tune it way down to about 165 as my LT threshold is kinda low. (I operate on ~1.5 kidneys, so higher intensity simply isn't possible for me.... Yet...) For outdoor running, it can automatically adjust your max heartrate and LT threshold. Seriously take some time and dig into the app and learn how it is computing metrics like that.

If accurate heart rate is important to you, get a chest strap that is compatible. The accuracy is much better than a a watch and the data doesn't lag as much. (I get better metrics about step speed loss and ground contact time balance as well.)

But yes, 180 is high intensity. At our age, we need to ensure that we get cleared by our doctors for high intensity stuff. (I don't know your full medical history, nor could I fully understand it.)

I have been running for over a year now, and am just now allowing myself to get into the 160's. However, the reduced blood supply to my left kidney (renal artery stenosis) can cause my blood pressure to spike hard. With lots of exercise and meds, I have that under control for the most part.

For me, as mentioned, I have underlying issues so getting up into the 180s could potentially be stroke territory. Over a year ago, I had a CT scans and MRIs on just about every critical bit of my body looking for the cause of my BP issues, so for now, I know there isn't anything in my brain that could pop quite yet. (The risk is still there.)