I am over 40 and I was recently laid off. My employer asked me to sign a waiver that I would not bring any claims against the company and I signed it. Does that mean that now I can't bring a discrimination claim against my employer?

Not necessarily.  Under the Older Workers Benefit Protection Act, 29 U.S.C. § 621 et seq., in order for a waiver to be considered valid, the waiver must be written in a manner that is "calculated to be understood," must allow the employee at least 21 days (in some cases, 45 days) to review the waiver before deciding whether to sign it, must provide the employee with some additional compensation or benefit to which he or she was not already entitled, and must contain other specific information.  The waiver must also provide that for a period of at least 7 days following the signing of the waiver, the employee may revoke the agreement.  In all cases when you are presented with such a waiver agreement, it is a good idea to have an attorney review the agreement before signing it.