75 y.o. here, resting HR ~46, standing astride the bike, ready to go, ~58, cruising ~115, LTHR ~135, 143 is about when things are not OK anymore and I'd black out if I went any harder. I start to pant ~138. It's just having a big old heart. Normal or at least certainly not abnormal. A rider 4 years older than I with whom I used to ride was about the same, which also rather amazed me at the time.