Theoreticly Poly and Polystyrene caps should last indefinately as long at they aren"t dammaged by heat or a corrosive liquid.....
I have re-used Poly caps that were over 40 years old (Orange drops and Tropical fish and Polystyrene) and they worked as well as new Caps and many were salvaged from equppment that had been badly dammaged from moisture and heat....
Electrolytics wear out because they use a chemical Dielectric that breaks down over time were Poly type caps use a Plastic/Polystyrene or a metalized film that doesn"t break down....
The Polystyrene caps in your pic look like they are in pretty good shape, in better shape than some caps I have re-used...
Cheers