They don't give prostate cancer tests to men over 70. In Biden's case, they gave him one at 72, and he was clean. He was in shape and working out on a steady basis. They had no reason to suspect he had cancer percolating.
The symptoms are similar to what age normally brings.,frequent urination, peeing at night, aches, and pains. You do not look at someone and decide that they have prostate cancer.