The lifespan of a gas water heater typically ranges from 8 to 12 years, although this can vary based on factors such as water quality, maintenance, and the specific model. Regular maintenance, including flushing the tank and checking the anode rod, can help extend the heater's lifespan. If your gas water heater is approaching the end of its expected life, it's advisable to consider a replacement to avoid potential breakdowns and increased energy consumption.