If you were to look at a home as a set of systems and components, there will be certain life cycles it goes through.
Years three through seven are prime time for a home, not years one and two as most would expect. It takes a year or two for the house to work out the "bugs." This is when the initial defects are hopefully found and corrected. None of the major components should show any ware at this point.
That's not to say that homes this age are not trouble free. At least most of the problems have surfaced and been corrected. The ground around the foundation may have settled and will need to be filled in. As well as any inferior materials will most likely showing them-self's and correction can be made.
Problems typically found in years eight through fifteen are about the same as those found earlier, only now manifest in a more serious manner. Sagging will show up if framing was not done correctly as well as foundation wall problems associated with faulty drainage or soil issues. Sidewalks and patios built on non-compacted soil will need repairing or replacing.
This is also the start of the first round of appliance repairs and/or replacement. If they have made it this far, at very least they are seriously out dated.
Chances are the water tank and air conditioning compressor will need replacement during this time period. The furnace, depending on maintenance, may need replacement as well.
Years 15 through 25 will probably be the big "replacement years." The roof rarely lasts more than 15 years. The gas furnace will be ready to be replaced, windows and siding, if not maintenance free will need attention.
Homes 25 to 30 are most likely enjoying there prime period because all of the main systems and components have been newly replaced. At this point the cycle starts over again.
Personally I have been in homes as old as the late 1700's and I am always amazed at the ingenuity of the upgrades through out the years. Systems and componants come and go but a well built and maintained home can last 100's of years.
Written by, Hans Cramer of Cramer Home Inspection Group, Inc.