My 13-year-old water heater just (late Dec.) blew its drain valve clean out. Happily, the garage drains well. Temporarily took out the adjacent furnace the day before temperatures plunged to 15 degress F.
Looking at my records, the previous water heater lasted about 13 years also.
I think I may start replacing at the ten year mark, even though there might be a little life left in them.