What is the clubbing age in Japan?

I'm going to Tokyo this summer with my friend. We're both 18 and we're looking for really good nightclubs to go to that play good trance music. I read that Womb requires everyone to show ID. Would our passports work? Would they have a problem with our age? We're used to the over 18 clubs here in the states, but they make sure you can't buy alcohol.

Alcohol and smoking is allowed from age 20. Many municipalities and the metropolis of Tokyo have curfews on minors below 18, meaning that they are not allowed on the streets and in certain establishments without a guardian after a certain time in the evening.

In case of Tokyo, I think that people below 18 are not allowed on the streets, in karaoke places, game centers etc. after 11pm. But I think there are no curfews for people 18 and older.

I have been to clubs a couple of times in Tokyo when my friends and I were 18-19 years old. The age for entering Womb is 20 but they let us enter even if they looked at our passports.
Once a girl wasn't allowed to enter because she wasn't 20 years old. It's weird because there were many others in our party that wasn't 20 either but could enter anyway..
They don't check ID in the bars at the clubs.
They never check ID at convenient stores or resturants either.
Guess they have problems with deciding foreginers age.
Many times some Japanese get really chocked when I tell them that I was only 19. They though t that I was around 25-30 years old.

Yeah i had the oposite problem when i was there i look young and im actually 21.

I bought beer etc but no one id'd me or anything i wouldnt be able to understand them anyway lol!