Can I exit at Beijing airport? I am 17 years old Mongolian. I am travelling from London to Mongolia.

So you just transit in Beijing, right? Can you tell where you are from? People 51 countries enjoy 72 hours free transit in Beijing. During their transit, they can leave the airport as they wish. People from other countires enjoy 24 hours free transit. If they plan to exit the airport during their transit, then should apply for a stay permit.