Are 5 year old skis in good condition outdated, or are skis evolving slowly and should be good until a big breakthrough?
I've owned a lot of skis. Usually they just get obsolete ("outdated"), rather than wear out: does that ski still have a "wow" factor for me, or not?
Sometimes I'm not really conscious of this, but I just stop pulling that ski out for the day. It's a bit unpredictable just when a ski goes unused or gets outdated. Maybe it mostly has to do with what other skis are out there: does the ski still do just as well or better than other skis in its category or width? That probably decides it, over time.
I like to demo as many new models as possible, every year, to get a sense of ski improvements. I already have multiple skis I like in each general ski category, but they all ski differently. Usually, I add a new pair when I notice that the ski I'm demoing or borrowing has a "wow" factor, that is, it does one or more things differently, and better, than any ski I already own or have tried. For me to want to buy it, a ski has to have that sort of improvement to it, that "wow" factor, that puts a big smile on my face. Some years, there may be only a ski or two I experience this way. And other years, there may be too many, for me, groundbreaking skis to be able to or want to buy all of them. (And overall, to me, skis are getting more dialed in all the time!)
By the same token, I keep - and use - a pair of skis if it does not become worn out, obsolete, or "outdated." If a ski still does at least one thing better for me than any other ski I own, and maybe better than any other ski I've tried or know of, that ski is a keeper, not obsolete. So there are skis I still use regularly that are more than a dozen years old. (The Stockli SR XXL 78 is a ski that comes to mind.)
Since I do my own tuning, including base flattening, edge prep and waxing, my skis don't tend to wear out very often. (Especially if they are Stocklis.)
Having a lot of skis by now also means I spread out my days on a lot of them, and they are that much less likely to wear out before they become obsolete, if that is what happens to them.
Seems like we are living in a golden age of skis right now, whatever else is happening.