I think I have a little the reverse issue to Asterix. I'm a few years younger than you, but can't get my heart rate above about 140, and that's on a good day. This is generally going flat out on Zwift. But my resting rate is low, like others here, and so I think is my blood pressure.
I've had a heart bypass, so the drugs will have some effect. List Asterix, I took little interest until recently (when I had the op, basically), so I don't have historical data. But I've never been able to push the rate up on hills and so on. I just plod, even in time trials. So my guess is that maybe I've always been a bit like that. I do realise that there's more to hill climbing than heart rate; it's just that it doesn't seem much different now from before.