How to make sure the girl is of legal age?

I am visiting Hong Kong and going to visit some of the famous buildings. How do you ensure that the girl is of legal age. Since these are not establishments there is noboby ensuring that the girl is above the age of consent. Can you ask to see some form of id? Also I am a tourist going there for 2 weeks from South Asia and not familiar with this place. Is the normal price HK$400 for 30 mins and can I pop multiple times? and is there anything that I should be careful about?

I guess if you go to a 141 walkup building the girls there have to rent a room and there is no way someone under 16 years of age would be able to rent there. Correct?