The greylag develops through several distinct stages, beginning with the embryonic stage where the embryo develops inside an egg. At birth, the young's eyes open, and they enter the chick stage, which lasts from 1 to 2 months and is characterized by a covering of yellow down. Following this, the species enters the rapid growth post-chick stage, lasting from 2 months to 2 years. The greylag reaches sexual maturity at an age ranging from 4 weeks and 2 days to 3 years. The adult stage, where the bird is capable of reproduction, lasts from 2 to 25 years. A typical lifespan for the species is from 15 to 25 years, although the maximum recorded lifespan is 28 years. The theoretical lifespan ranges from 22 years and 4 months to 31 years and 11 months.