Simple age verification?

I am about to build a site for a liqueur brand and have to create a simple screen that asks if the user is of the right age. This does not have to be linked to a credit card, just a simple yes or no screen. I am thinking this would probably be done via a cookie, but I am not sure.

Somehow it would have to work where it gets checked each time anyone goes to the site, regardless of the entry point. So for example it would get checked on mydomain.com, but also on mydomain.com/about, or mydomain.com/somethingelse. The yes or no screen would of course only show the first time the user came to site. Via what technology would I do this? Cookie? Can cookies have an expiration date?

I would love some comments or direction on how this is done best.

Thanks a lot!