Life span of an average flexible water hose
The life time depends on various factors and so it is not possible to give a definitive answer. 

If the considerations are for an outdoor typical "garden hose" then here are some factors that will affect hose life:


How long the hose lays out in the direct sunlight.
Temperature of the environment where the hose is stored.
How many times the hose is driven across.
Number of times the hose is uncoiled and coiled back up.
Amount of time the hose is left under pressure with the nozzle at the end closed.
Material the hose is made of.
Thickness of the hose walls.
Diameter of the hose. 
Whether the hose has embedded braiding.
Quality of the end fittings.
Amount of times the end fittings get stepped on or banged on concrete.
Number of squirrels or gophers that chew on the hose.
Number of times run over by the lawnmower. 


If the consideration is for a hose used indoors such as in a shower or hand held shower head at a sink there would be a different set of criteria. Here are the ones I can think of for that situation:


Water temperature through the hose.
How much the hose is flexed in normal usage.
Number of times when the hose is forcefully jerked when used as emergency 
Material the hose is made of.
Thickness of the hose walls.
Diameter of the hose.
Whether the hose has embedded braiding.
Quality of the end fittings and types of crimp strain reliefs there are near the end fittings.