Questions & Answers about Min morfar er firs år.
Why is it morfar instead of a general word for grandfather?
In Danish, you specify which side of the family a grandparent is on by combining the parent words. Morfar literally means mother-father (maternal grandfather). A paternal grandfather would be farfar. The same goes for grandmothers: mormor and farmor.
How does the number firs mean eighty?
Danish numbers from 50 to 90 are based on a system of counting by twenties. Firs is short for an old word meaning four times twenty. You just need to memorize these forms as vocabulary words: halvtreds (50), tres (60), halvfjerds (70), firs (80), and halvfems (90).
Why don't we say firs år gammel like we say eighty years old in English?
You actually can say firs år gammel, but it is very common and natural in Danish to just drop the word for old (gammel). Saying someone is firs år (eighty years) is perfectly complete on its own.
Why do we use min here instead of mit?
The possessive word for my has to match the gender of the noun it belongs to. Because morfar is a common gender word (an en word, en morfar), you use min. If it were a neuter word (an et word like et hus), you would use mit.