One thing you can do is set things up quarterly by the season.. makes perfect sense.Look water heaters, cooling systems, boiler systems,schedule filters on those systems to be changed or inspected.exterior roofs, siding, windows a good general inspection spring and falllandscape grounds, parking area's including trash areas at least 2 times a year for needed replacements or lot line painting, or pot hole fixing..You should get into the units for a quick look see at least 2 times a year.. if not, be sure and schedule one before you renew a lease to make sure the upkeep is to your satisfaction.Just don't replace all the stoves at the same time or fridges,, then you'll have them all die again at the same time.. do appliances as needed.. and save some $$ so you've got that covered. 

Age is not necessarily a part of the correlation, other than upkeep costs. 

I was lucky and bought it in 2013 and the rents cover my mortgage and general upkeep whilst the value has gone up almost 50%.

When you have rental property, you will have the ability to itemize the expenses for the upkeep, utilities you pay, general maintenance, property mgmt fees, mortgage interests, and other misc. expenses.On top of that, you also get to use depreciation over 27.5 years.

The renter/buyer will assume all maint & upkeep of the property.

Condition of the property is always a major factor and carries significant weight.

I've heard that good contractors are worth their weight in gold, I'd appreciate a suggestion!

A person walking on the roof will add a significant amount of weight to one small spot, increasing the risk of structural failure and personal injury.

Anyway back to the deal - we looked for several months and kept finding deals in the 41-45 month ROI, anything under 40 months was a bit ghetto for us and/or needed major up keep and repairs.

I may end up keeping one of my cars instead, in order not to make tradeoff mistake.