It's the law...we can't allow minors to buy our wine, but we sure hope their parents and guardians are interested!

from the California Alcholic Beverage Control Act

16. Distribution to Minors
A licensee has no inherent right to sell liquor and his engaging in the business may legitimately be subject to rigid conditions that will limit the possibilities of sales to children under 21; the words “immediately prior,” as used in B&PC§ 25660, are words of limitation in time, and the act of questioning a minor and seeing some proof of age two or three weeks before a sale is not “immediately prior” to the sale. Farah v. Alcoholic Beverage Control Appeals Board (1958, Cal App 2d Dist) 159 Cal App 2d 335, 324 P2d 98, 1958 Cal App LEXIS 2003.