性成熟
Sexual maturity and thus the earliest age at which mammals can reproduce varies dramatically across species. Members of the rodent family Cricetidae can reach sexual maturity in 1–2 months, e.g. the Norway lemming ("Lemmus lemmus") in 39 days. Many dogs (family Canidae) and bovids (Bovidae) take about a year to reach maturity while primates (including humans) and dolphins (Delphinidae) require more than 10 years. Some whales take even longer, with the longest duration being recorded for the Bowhead whale ("Balaena mysticetus"), which reaches maturity at an age of only about 23 years.