Anja is "underage" because she is a few days short of her 21st birthday. She says she will be an adult "next Tuesday at 3:00 o'clock." But a person always gets a day older at midnight. (This could only happen if Anja were born in a time-zone 9 hours ahead of Germany, such as, say, the Solomon Islands between Australia and New Zealand -- then 3:00 p.m. Tuesday in Germany would be 12:00 a.m. Wednesday, a new day, in the Solomon Islands. But in the movie, it was never hinted at that she was born in a different time-zone.)
At about 30 minutes into the film, secretary Wilma is typing using the 2-finger method.