CA Minors *can* sign contracts
See "Contracting With Minors", State Bar of California, Business Law News Issue 4, 2008 by Robert N. Pafundi 
Since 1971, the age of majority in California has been 18 for both men and women. The general rule is that a minor may make a contract in the same way as an adult, subject to the power of disaffirmance. See Family Code § 6700.
However, some contracts with minors, such as those “relating to real property or any interest therein” or “any personal property not in the immediate possession or control of the minor” are void from the time they are entered into ( Family Code §§6701(b) and 6701(c)).
In addition, a minor is also prohibited from delegating the power to contract on his or her behalf. (Family Code § 6701(a)).
But most contracts, except those that are statutorily prohibited, may be “disaffirmed by the minor before majority or a reasonable time afterwards or, in the case of the minor’s death within that period by the minor’s heirs or personal representative.” Family Code § 6710.
The effect of this rule is that the minor can unilaterally void or disaffirm the contract, or decide to enforce it against the other party (unless the other party is also a minor).
The minor can disaffirm the contract orally or through an action that manifests an unequivocal intent to repudiate the contract. See, e.g., Spencer v. Collins (1909) 156 Cal. 298, 303; Celli v. Sports Car Club of America (1972) 29C al.App.3d 511, 517. See also Pereira v. Toscano (1927) 84 Cal.App. 526 (holding that an oral statement was sufficient to disaffirm a contract).
The minor, however, cannot disaffirm parts of a contract and seek to enforce its other provisions. It is all or nothing. See Holland v. Universal Underwriters Ins. Co . (1969) 270 Cal.App.2d 417, 421.
The generally protective approach to minors who contract is warranted. Even in our media - saturated culture where children seemingly mature faster than they used to, children are substantially more vulnerable than adults with whom they contract. But as children have wielded more economic power, and as some contracts with minor actors and athletes can involve tens of thousands if not millions of dollars, California law has developed tools that increasingly give those contracting with minors the ability to enforce those contracts.
The most straightforward way to enforce a contract with a minor and overcome the minor’s common law right to void the contract unilaterally is to obtain pre-approval of the contract from a superior court. Family Law §6751 establishes an underutilized procedure for obtaining such approval.
Under that section, “[a] contract, otherwise valid, . . . entered into during minority, cannot be disaffirmed on that ground either during the minority of the person entering into the contract, or at anytime thereafter, if the contract has been approved by the superior court . . . .” A Superior Court has the authority to pre-approve the contract if it is located “in any county in which the minor resides or is employed or in which any party to the contract has its principal office in this state for the transaction of business.” Thus, a business headquartered in any California county may seek court approval from its local superior court regardless of where the minor lives or works.
 http://pafundilawfirm.com/Articles "Contracting With Minors: How California Lawmakers and Courts Deal with Adults Who Enter Contracts with Minors"