Soon I will retire (July 2021 – retirement age: 51), and will have 6 investment properties with 5 paid off.

It's in great shape for its age but has been sitting for a while.

., square footage, age of home, comps in neighborhood, etc.

Youd be surprised what you can still do at your age!

As a new Rental Investor I thought knowing the recently rented homes gives me an idea about the demand, Age on the market, median $/sft, quality of tenants, etc. in the neighborhood before making decision on looking for properties there.

To be a successful real estate agent and investor at a young age, you are going to have to really be knowledgeable on all aspects of real estate investing.  

One story v. one story, age, same subdivision or as close as can be, same schools and district, etc.

But at our age you're up several times during the night for those annoying toilet trips that makes the ensuite bathroom I added an absolute necessity.

The age of the house also doesn’t matter. 

Depending on the specific property, I'd expect higher construction costs due to the age of the properties.