Winter Training in RP, Saturdays

Given that I am 51 and deducting my age from 220, my rule of thumb max ought to be 169 and so I came pretty close to it but I suspect that my actual max is higher. What happens if you exceed your max or is max as high as you can go

It is almost impossible to go to your exact max HR and it is not that important anyway. More important is your Threshold HR, simply spoken the HR where your body can just break down as much lactic acid has produced in your muscles. The more your train the more power you can generate at your threshold HR. The value itself wont hardly be changed by training.
Best thing to find out on a bike is actually on a longish stady climb. You will find yourself working at threshold HR after a while almost automatically.