So most investors just throw in the same expense factors no matter the age of the property.

At his age, it’s not like he can start investing or manage a property, so I’m trying to figure out how to nurture this interest without overwhelming him. 

Then divide that cost by the amount of time between now and then and that's how much you should be putting aside for Capex.For general maintenance, the age and condition of the building will play into that.

Are there any investors between the ages of 18 and 25 in this group?

We plan to rebuild, but our neighbors are aging and do not wish to go through a rebuild.  

The house's age isn't so important as the age of the systems in the house.

Within that area what does your demographic research tell you about the age range? 

Mainly I’m trying to avoid “aged poorly design” glassblock walls, small bedrooms, older windows (wood/aluminum, single pane), aluminum patio covers, and to a lesser extent landscaping.

I built my first modern 7 years ago and like you agree that some (not all) moderns will age out.

All North DFW has the highest appreciation while South DFW will be giving you the better cash flow.If this is your first rodeo, then I would suggest to be close home if you are also planning to self-manage.Then the age of the properties and access to highways.