Ask HN: How to streamline private beta email signup for age-verified app?

Hi HNers, I'm getting close to putting up a landing page for a pre-release game I'm working on. I want to allow people to enter their e-mail address to be notified of the private beta. The complication is that the eventual game will need to be age-verified. E.g. the landing page won't have nudity, but the game will. So, how do I create a streamlined landing page where interested people can provide an e-mail address, without forcing them to first click through a bunch of legalese and age verification? I'm assuming that some people who would provide their e-mail addresses (without knowing the product's adult themes) would be surprised and annoyed to then get an e-mail with links to an adult game. I don't want to be a jerk. Finally, I don't want to create the impression that I'm advertising the game to minors, for whom it's not intended. So, how to balance simplicity, with non-douchebaggery?