It's very difficult to guess one's age. Alko knows this too well. That's why the company encourages all under 30-year-olds to prove their age at the counter. 

To show how difficult Alko's employees task is, we riddled the audience with a musical age test where those about 30ish get to shine as they spent their youth listening to these songs. But because music taste or wisdom don't prove age, you should always prove your age with appropriate documents.