There is no such thing as statue of limitations of debts. Debt starts from the time the payment is delinquint. However, in the state of Texas, residents are protected under Texas state law and cannot be sued for their debts. This is goverened by both state and the FDCPA laws.
Texas Civil Practice and Remedies Code Chapter 16. Section 16. 004(3) limits the time in which an action may be filed to collect a debt to four years. The four year limitation applies to debts created by either an oral or written contract. Some acts (such as acknowledgment of the debt) may extend the time beyond four years.
Some debts may be uncollectable or capable of simple resolution. You do not have to deal with an abusive debt collectors. The Texas Civil Practice and Remedies Code provides a 4-year limitations period on these types of debt. The SoL begins after the day the cause of action accrues.