From Consumer Wiki
A bank is not obligated to pay a check that is presented more than six months after its date of issue, but may do so if it wishes. (Commercial Code § 4404)
There is no law that prohibits a check writer from postdating a check (giving it a date in the future). However, a bank has no duty to respect that limit, and may pay the check in advance of its stated date, unless the customer gives notice to the bank of the postdating, describing the check with reasonable certainty. (Commercial Code § 4401)
It is a violation of the Fair Debt Collection Practices Law for a debt collection agency or a creditor who regularly collects its debts to deposit a postdated check before its due date. (15 USC 1692f(4))
"The presentation of a postdated check is not subject to the civil or penal sanctions" that would normally apply to someone who wrote a check with insufficient funds because the postdated check promises "to discharge a present obligation at a future date" and that money would be available to meet the debt when the check is cashed.
Should the question arise the check is "postdated", there should be no problem if the debtor wrote the words "postdated" above the date of any of the checks submitted, however, without this kind of documentary evidence, it may be difficult for the debtor to prove the checks were "postdated". A judge might have to see whether the checks given in evidence bear sequential serial numbers, or appear to have been written at the same time. Such evidence infers the "checks" were postdated.
Special rules apply if a check postdated by more than five days is given to a debt collection agency or a creditor who regularly collects its own debts. The payee must give notice to the check writer at least three days, but not more than ten days, prior to depositing. (15 USC 1692f(2))