Should doctors be on ob night call past 55? My hospital has a policy but I want my doctor.

It's ok. Many ob's take night call after 55. It will probably be hard to circumvent the policy however depending on the hospital. I don't think this is super common.
This is unAmerican. I think it is totally wrong for a hospital to dictate who can deliver babies, or do anything else, as long as that provider has board certification. Hospitals are very much over stepping their boundaries. They are afraid of "malpractice". There might be a reason that they don't allow this doctor to do deliveries any longer.