The statue of limitations for a debt collector to attempt to collect a debt is 6 to 7 years.
After 7 years the debt collector can still try to collect it but they can't sue you for the debt after 7 years is up.
That is unless you respond to the debt collector and try to work out payment arrangements with the debt collection agency then the clock starts ticking again and they have another 7 years to attempt to collect and can then sue you in court for the debt.