It will vary greatly with the type of service. Lots of idling in hot weather will shorten their life compared to less stop and go driving in milder weather. Elastomeric materials typically degrade exponentially with temperature.

Also, keeping the outside clean and free of petroleum product residues will help extend life.

As a rule you can inspect the hose visually and "by feel". A degraded area of the hose will generally manifest as a soft spot before it blows.

Most "modern" elastomeric materials - say since the mid to late eighties - will last a lot longer than those from earlier eras.

Duke