Sewer pipes can be damaged in many ways.  The older the plumbing, the easier it is for those pipes to suffer damage.  In Texas, we deal with expansive clay soils which can wreak havoc on all types of underground piping.  Problems with pipes include:

Tree root infestation

Sagging or bellying

Offsets

Breaks

The age of a home does not necessarily tell the entire story.  Older homes might have had newer plumbing installed, or newer plumbing might only have been installed in certain areas.  An agent and the homeowner (depending when the repair was done), might have no idea as to the types or conditions of those pipes and or repairs.  When you make a large investment and purchase a home, you do not want to discover you need up to $20, 000.00 for pipe repairs after you have moved in.  

A relatively inexpensive way to protect you and your investment is to get a set scope inspection.  

A sewer camera inspection is an attempt to gain a better understanding of the general condition and integrity of the main drain laterals. They are viewed were accessible from the house to the street or septic system and directly under the house. The sewer camera inspection looks for visible defects, including obstructions, offsets, bellies, breaks, rust and scaling, and other visible conditions.