Legal Question in Business Law in California

Do you mean you have issued checks to vendors which haven't been presented for payment? Here are some laws on the topic:

Commercial Code section 4404 gives a bank discretion to honor, or to refuse to honor, a check that is presented for payment more than six months after its date.

The Code of Civil Procedure provides a general statute of limitations for initiation of suit on a written contract of four years from date of breach; for an oral contract, the time is two years. CCP sections 337 and 339, respectively.

Commercial Code section 3118 provides statutes of limitations for suits involving negotiable instruments. However, I'm doubtful that any of them apply to your question, and indeed I don't think what you're looking for is a statute of limitations. Statutes of limitations deal with when a lawsuit must be brought, not when a check can no longer be cashed.

Conditions under which a party may request its bank to "stop payment" are set forth in Civil Code section 1719.

There is no law I know of that flatly says a check older than X days, weeks, months or years is no longer valid. Whether to write off the liability is a question for your accountant.