Any tips about age restrictions?

Hi there

I'll be travelling to Japan with friends and half of us are 19 (the other half are 20).

Seeing as the legal drinking age is 20, are there any other typical tourist/every day kind of things that we should be careful about (i.e. aren't allowed to do)? Any restrictions for places/activities etc.? Would there be issues for restaurants that also serve alcohol?

Any warnings would be greatly appreciated, thank you!

You are not allowed to smoke cigarettes or drink alcohol younger than 20 yrs old.
You are not allowed to purchase public gambling tickets(horse racing, motorboats, Keirin and autorace) if you are younger than 20 yrs old.
You can purchse pornographic goods and services if you are over 18 yrs old.
Take you ID with your photo attached always if you visit such places with age restriction, you may ask to present your ID if you look younger than legal age.

Most clubs have strict ID checks. On the other hand, restaurants, bars, and izakaya (Japanese-style pubs that serve food) very rarely check ID. (In fact I've never heard of it happening.)

If you're buying beer or canned cocktails at a convenience store, the cashier will ask you to press a button on the cash register that affirms that you are twenty years old or over.

Just in case, remember that you are supposed to have your passport with you at all times anyway.

Thanks for the help guys! You're all awesome :)