Should docs be subject to law or regulation as pilots concerning age/training to avoid catastrophic errors on patients? why 85 yrs old doc continues?

It depends on doc: I agree with you that older doctors should be evaluated to make sure they are still able to perform all of their duties, but i also recognize that there are many older doctors in superb health who are doing fantastic work. Most hospitals have policies for re-evaluating their staff every couple years to see if someone shouldn't be continuing to practice at their current level.