Which kind of pain? Muscle pain I don't mind much, it goes away after rest and lessens with conditioning. Fatigue, which some people find painful, ignore to the extent possible. Pain in the joints is a warning, which demands a period of recovery. Neurological or skeletal I'd monitor pretty closely and seek medical advice.

If someone tells you, you should be able to ride X miles or Y hours with no pain then they're speaking for themselves, not you are anyone else. If I've been doing 30-40 mile rides then 50-60 is going to end with some discomfort, maybe pain. If I've been doing 60-80 miles then no, no pain. Though it's more about how much time the ride takes. An hour and a half, two, three, whatever it is that you ride frequently you should be OK with, but pushing it a half hour longer you can expect some discomfort or pain.