When mice are 12 weeks they adults?

Yes, mice are adults at 12 weeks. Mice have a short lifespan compared to humans, with an average lifespan of 1-2 years. They reach sexual maturity at around 6-8 weeks of age and are considered adults by 12 weeks. After reaching adulthood, mice continue to grow and develop until they reach their full size at around 6 months of age.