doubt if you even have to be of age.

If the petition is to get a candidate on the ballot or to get an initiative on, then every state I know of requires that the signers be registered voters, and they check the names against the voter rolls before they certify the petition.

Apologize if I caused any problem.

California Petition Signatures

Only persons who are registered, qualified voters at the time of signing are entitled to sign the petition. A person can only sign a petition that is being circulated in his or her county of registration. If a petition circulator is a registered voter, he or she may sign the petition he or she is circulating. (Elections Code §§ 105, 9020, 9021.) Each signer must personally place on the petition his or her signature, printed name, residence address (or physical description of the location if there is no street address), and the name of the incorporated city or unincorporated community. (Elections Code § 100.) None of the above may be preprinted on the petition. Each signer may sign an initiative petition only once. (Elections Code § 18612.)

they should know.