It really depends on what it is and what you're doing with it. If you race a dirt bike in motocross for any number of years anything past 5 years of racing on it will be far past the point of being worth it to repair.

Naturally, if you're a trail rider and don't abuse it than these things can't last 30-40 years with light repairs.

Also generally speaking have you rode a 20 year old ATV or watercraft compared to the recent ones? It's a totally different experience on the body alone lol