When does a hamster grow up?

Hamsters have short lives and grow quickly; they are sexually mature around 21 days and fully developed by 2 to 3 months. After 3 months, keep one hamster per cage, or their breeding ability may shock you, and frequent breeding badly harms their health and the offspring’s quality.

Hamsters are adults from 3 months to about 1.5 years, and enter old age around 1.5 years.