I've recently bought a house that is about 20 years old. Within a week of moving in, I've found if too much water is going through the system (ie after I've showered, done the dishes, and a load of laundry), all drains (including floor drains) start overflowing. I've tried plunging, but it doesn't seem as if that's the problem. The house is also built on a slope near the coast if that helps, and was vacant 6 months before I bought it!
Abbey