Cal. Bus. & Prof. Code § 23790.5
(b)
(c) Subject to the restrictions and limitations of subdivision (b), this section shall not prevent a city, county, or city and county from denying permission, or granting conditional permission, to an individual applicant to engage in the concurrent retailing of motor vehicle fuel with beer and wine for off-premises consumption pursuant to a valid conditional use permit ordinance based on appropriate health, safety, or general welfare standards contained in the ordinance if that conditional use permit ordinance contains all of the following:
(d) Notwithstanding any other provision of law, establishments engaged in the concurrent sale of motor vehicle fuel with beer and wine for off-premises consumption shall abide by the following conditions:
(6) Employees on duty between the hours of 10 p.m. and 2 a.m. who sell beer or wine shall be at least 21 years of age.
The standards contained in this subdivision are minimum state standards which do not limit local regulation otherwise permitted under this section.