The reason I am saying to ask your aging parents to downsize is to do so while everyone still has the energy to help sort, donate, and move into something more manageable.
My parents were in their mid to late 90's and still glued to their single family house. Once Mom passed a couple of months ago and Dad decided last month it was a good time to move to Independent Living, he now wants to sell the house ASAP.
Dad only took what he needed for his new apartment.... there is still a lot of furniture left in the house, kitchen cabinets with lot of cookware and glassware, not to mention the stuff in the garage, and everything in Dad's workshop in the basement [found a very old computer down there] and more stuff. I already tossed out a lot of clothes that I couldn't donate, and have bags of clothes to donate. I do plan to call an Estate Sale person to sell the items. But I need to throw the junk out first.
Whew, after work I am tired and that only give me maybe an hour each day to tackle one corner of one room. Oh my gosh, all the dust !!! Let's not forget about all the paperwork that ones elders keep. Like warranty booklets for things they no longer have. I dragged home several dozen 3-rings binders with financial info, as I now need to do the finances as Dad doesn't want to bother with it. Oh fun.
And there are things I would like to keep so now my family room at home looks like a flea market :P And there is more to cart home when I get the energy. Oh my gosh, as here I was trying to limit the things I have as I am senior myself, and would like to downsize before too long. It's hard to part with things that were part of my growing up.
So, once your Mom and Dad start to slow down, and you start to notice that they aren't keeping the house up, try to get them to sell and move into something smaller [it can still be a single family house but half the size], that way they would need to either donate, sell or toss out "stuff". I know it won't be easy. I would try to get my Mom to donate items, and to her that was one knick knack each year.... [sigh].