Is a 10 year old debt valid to pay if I'm on disability?

Not enough information. What kind of debt? What does disability have to do with the debt?

Your moral obligation to pay the debt nevers goes away,but if the debt is 10years old the sol's may come into play meaning you can't be sued BUT that does not mean they can't
Hound you for it. Is your disability social security or through a company plan.

Yes, it is valid. Of course it's probably been written off by now. Have there been any attempts to collect from you lately? If anyone attempts to collect on it, inform them that you are on disability. If they persist, you may have to file for bankruptcy.