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The worldwide average age of menarche is very difficult to estimate accurately, and it varies significantly by geographical region, race, ethnicity and other characteristics, and occurs mostly during a span of ages from 8 to 16, with a small percentage of girls having menarche by age 10, and the vast majority having it by the time they were 14. [3]
The average age of a girl's first period is 12 to 13 (12.5 years in the United States, [6] 12.72 in Canada, [7] 12.9 in the UK [8]) but, in postmenarchal girls, about 80% of the cycles are anovulatory in the first year after menarche, which declines to 50% in the third year, and to 10% by the sixth. [9]
The average age of menarche is 12 to 15 years. [1] [8] However, it may occur as early as eight. [2] The average age of the first period is generally later in the developing world, and earlier in the developed world. [3] [9] The average age of menarche has changed little in the United States since the 1950s. [3]
Called menarche, the first period occurs at the age of around twelve or thirteen years. [8] The average age is generally later in the developing world and earlier in the developed world. [42] In precocious puberty, it can occur as early as age eight years, [43] and this can still be normal. [44] [45]
The average age at which puberty begins may be affected by ethnicity as well. For example, the average age of menarche in various populations surveyed has ranged from 12 [58] [59] [60] to 18 years. The earliest average onset of puberty is for African-American females and the latest average onset for high altitude subsistence populations in Asia.
Spermarche, also known as semenarche, is the time at which a male experiences his first ejaculation. [1] It is considered to be the counterpart of menarche in females. [2] [3] Depending on upbringing, cultural differences, and prior sexual knowledge, males may have different reactions to spermarche, ranging from fear to excitement. [4]
The typical age of legal majority is 18 years in most contexts, although the definition of majority may vary by legal rights and country. Human adulthood encompasses psychological adult development. Definitions of adulthood are often inconsistent and contradictory; an adolescent may be biologically an adult and display adult behavior but still ...
In females, gonadarche is responsible for thelarche and menarche (first menstruation). [4] Gonadarche should be contrasted with adrenarche. Gonadarche indicates that true central puberty has begun, while adrenarche is an independent maturational process only loosely associated with complete puberty. [5]