Haha, in languages that have a t-v distinction, (informal like tu in French and formal like vous) it can be a minefield. While on the whole younger people are informal and older formal, it is pretty weird in Hungary, their are companies like IKEA who use the informal as policy which offends older people, on the other hand my mother was like (around 40) "oh no I am officially old, someone used the formal to me" so there are other people who, because trying to feel young or something, insist on the informal. You never really know. You are 26 and visit another business trying to discuss a project or something and the other guy is also like 26 and you stare at him and think in a formal business setting I should use the formal... but it is not common for our age... what do. What usually happens is that whoever is considered the customer offers the informal.
The old etiquette was that the older person would offer the informal, often drinking a "per tu" drink.
If one person uses the formal and the other the informal consistently, this is called csendőrpertu, gendarmerie per tu, and highly demeaning / humiliating. Except between children and adults. We always called the teachers formal at school but they started only calling us formal around 14 when we were no longer children.
And then there is this stuff with names. Call people on a first name basis, or Mr. Surname and Ms. Surname, but just calling someone surname and nothing else is for some reason offensive in Hungary. Well, not as much offensive as kind of commanding, authoritarian, military trainers or stricter teachers would do this. EXCEPT that somehow it is okay for kids doing this to each and they do this all the time. Really weird.