The first is condition which can be cured by regular periodic maintenance. Three primary points to focus on: foundation, exterior, and equipment.
The foundation, whether its a pier and beam or a slab (most common in Ellis County), will shift and if not cared for will cost more in sales price reduction than it would to fix the problem. Most foundation companies will come out to give you a free assessment. Get more than one.
Exterior maintenance - painting, siding, roof, and brick and mortar repair will not only give your house better curb appeal, but will extend the life of the house. The chief concern is to keep water out. Moisture accumulates between the outer and inner walls if the outer surface is damaged. Paint is there to keep moisture from soaking through - masonite siding resembles oatmeal when it gets wet and will disintegrate.
Equipment, (ex. water heater, HVAC unit, kitchen appliances) will wear out over time and need to be replaced periodically. Here again maintenance will promote a longer life. This can be as simple as changing the filters out monthly, (which reminds me I need to do that today).
The second way in which age comes into play is changing designs. Houses built in the late 50's through mid 70's typically have a small half bath for the master bedroom. Houses built in the 70's have fewer windows, plywood paneling, and wall paper throughout. These design issues are a form of obsolescence. They can be cured is some cases by updating. Open concept floor plans with large common rooms and small bedrooms were the vogue in the late 90's and well into the last decade. It appears this trend may be reversing as more people realize the noise level escalates when TV, pots and pans, and computer games are all competing for attention in the same open area. In this case, older houses with bigger bedrooms are coming back into fashion.
So, the age itself won't hurt the re-sale of a house. Feel free to buy the house that suits you, but keep it in good shape.