I rode around the hills near home. There are some great training areas, and other cyclists now and again can show me how it's done.
Some of the younger women are fast.
I've had a few missed beats lately, and with a low pulse rate, you tend to notice. An ECG test revealed no problems but you wonder if they look at it and think "OK - for a guy in his 70s . . )
Being a smidges off 74, the spinning classes mainly do it for me now, 6 or 7 days a week. As long as my heart beats to the tune (135 or so bpm, my neck is my guide, I can't read a fitbe) my breathing and cadence follows. I'm happy wi that.
They call it HIIT, and it's recommended for older guys. I am not the oldest there, and it's such fun.
Nor have I yet crashed a gym bike! That's the good bit.