https://en.wikipedia.org/wiki/Age_restrictions_on_energy_dri...
However, more relevant to the post, is that when you're ordering groceries online, you need to verify your age at checkout if you're buying stuff like alcohol (or energy drinks). It's trivial, and for a lot of people it uses the same authentication service that they already use to access their bank.
Edit: currently a voluntary but widespread scheme by retailers, proposed to be law. TIL
Also things are going to get hot at the next general election if you're following what just happened in this week's council elections.