Like most things folks want easy, simple answers. Unfortunately, there are no hard and fast rules. Aftermarket hose makers may tell you hoses should be replaced after five years. I suppose they know best how crappy their hoses are. I have found most OEM hoses can last quite a long time. Life time depends on type of coolant, cooling system maintenance and environmental conditions, such as ozone levels, etc. The answer is periodically check and replace as necessary.