A part of this is because I want to retire from my day job at age 40, so about 13 years from now.

The chance of water heater failure begins to dramatically increase at age five.

Age of properties?

However, if you had talked to real buyers, found out what they wanted, the price range, the locations, the age, the style they like and picked thier brain you'd know what to look for.

I would not offer him the whole 130K unless you are planning a buy and hold the property, but at best, depending on the property and its age and any problems, I would only offer him 100K, therefore leaving you with 30K in equity.

The main drawback is the properties age.

At my age, lol, I typically get 20 year loans.

You should consider adding other data points such as the % change in rental vacancy rates (help you determine if it's growing as a renter's market), total # of listings, % change in the total # of listings (helps determine if it's a buyers vs sellers market), and the age of inventory and % change in age of inventory (also helps determine if buyers vs sellers market).

With small residential properties, I usually just use rent/cost ratios and comps with my estimated cap rate as a distant third.Cap rates are more of a method of valuation, i.e. building in a certain area/age/condition should have an 8 or 9 cap or whatever.

Bill Bonds , if you were 64, I may feel differently, but at the age of 24, you could absolutely do better than 4.5% over the long term.