Birthday party place for a teenager? (Milan)

Hi All, can someone recommend an interesting/affordable place to host an ( almost) teenager's birthday party in Milano center? Protected content , preferably with some flexibility on how many people attend ( e.g. No exact headcount), preferably outdoors, maybe a fun restaurant with a possibly separate room /garden? Or any party places you are aware of that I can rent that are not limited to toddlers? I originally wanted to do a park party, but read several reviews that for 15 kids using picnic tables a city permit is required, and I don't have nerves/time to go through this type of hassle... Any ideas are highly appreciated!