The Statutes of Limitations in California expire after 4 years on written agreements and after 2 years on oral contracts. Make sure that you last paid on this account before the stated period in case you are considering the SOL factor.
If your debt is past the statutes, you can send a letter to NCO notifying the expiry. Send your letter through certified mail with return receipt requested. After the company has received your letter, they must stop all collection attempts.
Do not make a payment unless you are interested in paying it off and improve your file. The debt will come within the statutes upon a single payment and if you default, the company will enforce all sorts of actions for recovering the amount.