Norway has a tiered system, you can buy beer and wine when you are 18 and spirits once you reach 20. Over the week-ends most pubs that are licenced to sell spirits have doormen, who if in doubt, ask for identification - if you have no identification then you don't get in. If you have identification and are under 20 you will not get in, 18 to 20 year olds can only drink in pubs licenced to sell beer and wine.