Pretty simple really. At what age are you allowed to/no longer allowed to do things where you live? I’ll start (I live in Norway, will give numbers for Denmark as well, since i grew up in DK)
School starts: age 6, +/- a year, depending on season of birth and the wishes of the parents.
At age 12, danish parents may no longer change the name of the child against its wishes. A 12 year old dane may also be given very light, salaried work, such as a short newspaper round.
Mandatory schooling ends: somewhere around age 15 (9 years total in DK, 10 years in Norway)
At age 15, you may drive a small motorized bicycly (a moped?)
Age of consent: 15 in Denmark, 16 in Norway.
Legally responsible for your own actions: 15 in Denmark, not sure about Norway (probably no more than a year older, or the same age.). This does not mean that you will be tried as an adult if you commit a crime, but it means your crimes go to the police instead of social services.
Voting, and other political privileges: 18 in both countries.
At age 17, you may start taking classes for a drivers license. You may not actually take this test until age 18 (many time this so they take the test on their birthday).
Allowed to drink beer/buy cigarettes: 18 in both countries.
Allowed to drink stronger alcohol: 18 in Denmark, 20 in Norway (yes, that means that a 19-year-old can vote, but not drink. Nobody understands this bit.)
In Norway, an 18-year-old boy can start dreading a letter telling him to report for military sevice. An unmarried woman with no children or demanding career can start dreading the same letter at age 30. The letter for the boys need not arrive until they are well into their twenties. 18-year-old girls will recieve an “invitation to serve”, but for them, it is not mandatory. (service is something like a year, BTW, and its not difficult to get out of if you don’t want to. If you declare yourself a pacifist, they wont make you serve, for instance.)
So, what milestones apply where you live? Feel free to ad more, if you have them.