Tires and seals will eventually dry out and crack. Grease will also dry over the years and not lubricate as well. Your chains will pick up dust that'll cake into the lube.
The BEST way to maintain an old bike is to regularly attend to lubrication and wear items. And the best way to keep track of lube and wear is to ride.
The BEST way to maintain your riding skills is to ride regularly. If you go on a handfull of rides each year you will always be a bit sketchy.
The BEST way to maintain your right to ride is to ride regularly. If you give up riding 90% then you will probably be pressured to give it up 100%.
(I repeated the word "BEST" several times here as if it is the "One Right Answer". It may not be the One Right Answer for you, but it works best for me.)
"The belief that there is only one truth, and that oneself is in possession of it, is the root of all evil in the world."-- Max Born, Nobel Physicist