By far the worst issue with old homes is cast iron sewers. These last 25-75 years depending on soil makeup and use factors. A have deteriorated sections and they are expensive to fix. Home built post 1990 (and as early as the 80s) are built with plastic sewers (I forget the specific type). These systems will last almost indefinitely if not disturbed by an external force. My personal take is craftsmanship was better back in the day but homes are built to better codes now (think electrical). If I found an old home with new electrical and a new sewer, Id go for it in a heartbeat.