Rubber can last pretty long when stored in warmish garaged conditions with little sunlight UV to degrade the material. Just make sure you feel good "flexibility" in the rubber and look for rubber rot/cracks in the tread/sidewall. If those check out you'll be good to go. Five to seven years is a good area to be aware of rubber condition especially if they are subjected to harsh sunlight daily but there is no "hard" rule.
If there are signs of minor cracking, your winter tires will still be grippier in snowy/icy conditions than all seasons but just be mindful about what road condition challenges you tackle as they may not get you up a certain hill as they once did one or two seasons ago. You may not stop as fast too so just be on the lookout for tire sales if you can't afford full
Here's a test of what winters vs all seasons are like in very cold "dry" conditions.
You'll see that winter's advantage is when it's everything other than dry. Again if you're forced economically or space-wise to only run A/S tires just pick your battles wisely.
I have PSS on my car and I usually swap them out when snow is in the forecast OR if I know I'll be driving in conditions with any chance of frost/ice, usually at night. I don't drive in places that are ridden with huge potholes or sharp impact bumps so I don't worry much about cracking/damaging my summer rubber from impacts like that. Michelin recommends to not use PSS in low temps but I believe that is advice for the general population who don't think of scenarios like that. In dry conditions, my PSS have far better grip than my Blizzak LM60s, even below freezing, until precipitation is anything other than wet. Just use good calculated common sense on how rubber works and you'll be a step ahead of the weather.