I was diagnosed with high risk PC at 73. My General Practioner checked my PSA every year. When my PSA was 2.2. At 72 it was 2.8 and at 73 it was 3.8.
My doctor didn't like the trend and sent me to a specialist who found 4+4 Gleason. My Mayo radiation oncologist told me that the PSA is caused by the prostrate and prostrate cancer. If the PSA starts rising, it's the time to check it out if the PSA starts rising. By the way, my brother was over 75 and his doctor wanted to stop checking PSA. Since I had it, he asked to have PSA continued and last year was treated for PC. Keep checking it.
I listened to a panel of Urologists who talked about getting patients who stopped getting PSAs and they were finding patients with much more severe cases of cancer. Catching it early makes it much easier to treat.