Most hot water systems on average have a life span of between 10 – 15 years. If you replace valves and anodes within their schedule maintenance timeframes {valves 3-5 years, anode 5-7 years} you are greatly increasing the life span of that unit. Ive seen hot water systems that have been regularly maintain reach 35 years, which is a great return for investment.
When a hot water system reaches 8-10 years, like most things parts start break down. Sludge and silt that break down will flow into your shower, bath, basin, sink and all appliances.
It is important monitoring your hot water system visually and by sound as ageing occurs.