The simple answer to your question is - It Depends!
More Info: As All Zeolites are NOT the same, it depends on the origin of the Mineral you have installed. If it originated from Eastern Europe then it may well be close to end of its usefulness, South African source is a little better but not appreciably, Mexican and South American are a good bit better, but the Best by a country mile is that Zeolites originating from Australia. Why ? Its a function of hardness, as the first bunch are around 5 on the Mohs hardness scale (quite soft like calcaire nearly or like sand) http://geology.about.com/od/scales/a/mohsscale.htm whereas Mexican is nearer 6 (like glass) but the Australian source is the ONLY one which is 7 (similar to Quartz) which offers the longest life of any.
So, it depends on the Brand of Zeolite which can sometimes identified by the colour- so if yours is a reddish pink colour (Australian Source) then you're good for another 5 or so years at least as it will be largely as it was when you first put it in. If yours is beige/grey then it’s very soft and could well be starting to degrade into a powder which will eventually be worse than useless as a filtration media because it will 'clog and cake', so it could well be time to change.
So answer the question then hubby will have to take the lid of the filter and find out what is in there. While he is at it then regeneration of the Ion/Canton exchange properties is a good idea (normally done at the beginning of EACH season). More on that in the next thread.