My $00.02. For me IT DEPENDS on what type of riding and what type of bike I'd be using that tire for. Put an older tire on a track bike? NO WAY! Put an older tire on a 170 hp sport bike that will be ridden aggressively? NO WAY JOSE! But put an older tire on a dual sport bike that will not get ridden very aggressively? Sure, why not. Put an older tire on your CT90? Sure, why not. If you'll be wringing that RT's neck for all it's worth .......... NOPE, NEW RUBBER NEEDED. But if you'll be riding that RT at a leisurely pace .......... SURE, USE THE OLDER TIRE. I've actually taken a sander to an older tire that had a hard look/feel to it. Basically I was curious about it, and decided to "scrub it in" before I mounted it. I was surprised at just how sticky/pliable/supple the tire still was once the thin "hard rubber varnish" layer on the surface was gone. In several hundreds of thousands of miles on 2 wheels I've only had one tire failure that was "unusual". I was in the process of doing a "Fly-n-ride" from SoCal back to CO via the "scenic route" when the rear tire failed after a few thousand miles. I had an experienced m/c tire guy tell me that the tire had been "very hot" at some point and the rubber had "broken down". He theorized that it had been run lots of miles while it was pretty low of air generating a lot of heat. This picture below shows the delamination of the tire over on the left edge. You can see where the rubber is coming off in large thin flakes around the steel belts. The other side of the tire was just beginning to do the same thing. It was on a K1200GT. Weird. The tire went from "a lot of meat" .......... to showing cords in just a few hours of normal road riding. I asked the tire guy "was this due to age"? (The tires were 8-9 years old as I remember, as the bike had been mostly sitting for those 8-9 years). He said "No, tires don't fail like this due to age ......... this was from high heat." Again, only my $00.02 from my real world experiences.