Nightlife for eighteen-year olds?

I'm eighteen years old and Italian. I recently arrived in Tokyo and I'm thinking about going out with some friends at night over the weekend and I'm not sure if it is illegal or not. If it is, do you know of any other places I can socialize with other people my age? If it's legal, can you recommend me some places?

Thank you!

As far as I know, if you're under twenty you're allowed to go to cafes, restaurants, izakaya, and bars, but not clubs that allow dancing. There will be signage at the door for places that don't allow people under twenty.

Technically speaking you're not allowed to be served alcoholic beverages if you're under twenty, but I've never heard of anyone being refused a drink unless they're actually wearing a high-school uniform at the time. (On the other hand, clubs will generally card you before they let you in.)

As for meeting people outside the group you're with, bars tend to be most interactive, although sometimes you can meet people at cafes or casual izakaya. If you mostly want to hang out with your group, casual, inexpensive izakaya might be a good bet - they're focused on food as much as drink, and you can order non-alcoholic beverages if you like.

Meetup groups (meetup.com) are another avenue for socializing in Tokyo, especially if you find one that matches your interests, although some groups are better than others.