Longest is a 2001 Jaguar XK8 convertible that I have had since 2003. 15 years.
Shortest was a 1984 Ford Thunderbird TurboCoupe. My ex-wife just couldn’t drive it. Couldn’t get inertia and throttle modulation right. Constantly in and out of turbo boost. Made for a choppy ride. We had several fights about it. Had it for 17 months. Car was good, but it just wasn’t working out.
I tend to keep cars for a long time.