You can proceed to apply for the persons bankruptcy if th debt exceeds £5000. You do this by way of petition to the court. Go to www.gov.uk/apply-to-bankrupt-someone/overview for information. Happy to discuss. I hope that helps. Please leave a positive rating so that I am credited for my time.
If a debt is more than six years old it might be time barred and as such any attempt to pursue it would be invalid. See online the Limitation Act 1980. It is important that no acknowledgement or admission of the debt by the debtor has been made within the last six years and that no court proceedings have been commenced within that period. A creditor can still chase the debt but is unable to use legal proceedings in court to force the debtor to pay. I hope that helps. Please leave a positive rating so that I am credited for my time.