Please try to measure distortion of tube amp while adjusting bias/balance of the output tubes, and you’ll see how sensitive it is. Then please repeat the same after 50+ hrs. If you are luky, and your AB tubes are aging the same pace, then distortions will not increase much. There is a lso big issue with output transformers in the tube amp, depending on core magnetics, resistance of coils, symmetry etc you will get variety of imbalance/distortion/FR problems, which does not exist in SS
We've done that plenty of times. No measurable difference. You can avoid a lot of the imbalance issues in output transformers by using a Circlotron, since the issues in the transformer are usually related to DC components, which are minimized in a Circlotron. This is so successful that Circlotron amps made in the 1950s were class B and had no crossover distortion at all. However such amps are rare.
IME tube amps suffer less from corrosion than solid state. I've serviced literally thousands of amplifiers over the last 50 years. You can have a well preserved solid state amp that shows no signs of corrosion but its semiconductors are failing on that account. If a tube amp is given the same treatment its likely the only service it will need (in time) is filter capacitors.
About the only place I see your age argument holding any water has to do with filter capacitors. Because tube amps run warmer, the filter caps have a shorter life than in solid state amps. So 30 years instead of 35, unless the designer placed the filter caps in such a way that they really ran too warm.