Obeying the Rules
The Universal Commercial Code doesn't require a bank to honor a check older than six months. In addition, the Federal Reserve says a bank doesn't have to accept a check if it has reasonable doubt that the issuing bank will pay the amount. An old check creates that doubt. However, just because a bank isn't required to accept a check after six months doesn't mean it won't. Each bank makes its own policy for checks after that period.
Check the Wording
Some issuers have a time limit on their checks, such as "Void after 60 days." This is meant to encourage the recipient to deposit or cash the check quickly. However, the Universal Commercial Code doesn't specifically address the validity of those dates, and they can be ignored at the bank's discretion. Unless the issuer has an agreement with the bank to adhere to the shorter time span, the check will be honored for six months. However, to play it safe, ask the issuer if it's still OK to cash the check or if you can be issued a replacement.