During this time, have you send any demand notices? If yes, has the debtor responded confirming the debt owed?
Generally, the statutory limitation for starting action for claiming a debt in court is 6 years from the date the debt falls due. This may be "refreshed" where you send the debtor a notice to claim and the debtor affirms the debt, or from when the debtor last made payment: Limitations of Actions Act 1958 (Vic) s 5.