I'm continuing to educate myself there.

If the house is not habitable (regardless of the cause), then my understanding is that the tenants do not pay rent during the time the house is not habitable.Hopefully your insurance has a Business Interruption or Rental Interruption clause that you can invoke so that the insurance company essentially pays your rent during the vacancy period.Once the house is habitable, tenants should continue their rent payments.

what he might have done with a better smaller operation.

So to answer a few o your questions one being no you’re not too old to do this there a lot of people in this business from as young as 18 up to 70 and beyond so you can definitely operate in this space.

If mobile, what phone/operating system do you have?

Don't buy so much house/duplex that you can't have a life and continue to save money. 

Start small, stay local, find the pain, provide a solution and continue asking questions.

Assuming the higher end of the resale, that would give a nice chunk of money to keep doing deals - if you can continue to find deals in your area, flip or rent, you will do better from a COC return.

What plans do you have to continue to save or generate investment capital?

Assuming there are no looming big ticket items that I am aware of, would you/should I continue to save for reserves, or just maintain that reserve and replenish as expenses arise?