At what age do most boys and girls experience their first menstrual or ejaculatory cycle?

1. Why the headline numbers matter—and what the big 2024 menarche study shows

A large May 2024 analysis found the mean age at menarche fell from 12.5 years (1950–1969) to 11.9 years (2000–2005) and that the proportion of girls with early menarche (before 11) rose markedly, with very early menarche (before 9) more than doubling in that cohort ^{[1] [2] [3]}. These results demonstrate a measurable downward shift in the timing of girls’ first periods within recent generations and identify socioeconomic and racial disparities in that trend. The study links higher body mass index and broader environmental and social changes to this shift while noting these factors do not fully explain the trend, underscoring the complex, multifactorial drivers of earlier puberty in girls ^[2].

2. The male counterpart: what data exist on first ejaculation and why it’s less certain

Research on boys’ timing of first ejaculation is far less comprehensive and more heterogeneous. A medical review places most boys’ first ejaculation around 12½–14 years, tied to a year or so after rapid penile growth (no publication date provided in that review) ^[4]. Other sources report ranges from about 13 to 16 years, with a 2011 Andrologia study estimating a mean conscious ejaculation at 13.27 years in Bulgarian boys and a 2018 population study estimating averages near 13.4 years ^{[6] [7]}. These studies rely on self-report, recall and population-specific samples, producing wider uncertainty than the large, recent female-focused menarche studies ^{[6] [7]}.

3. Why boys’ estimates vary: methods, culture and biological markers

Estimates for boys fluctuate because studies use different markers—self-reported first conscious ejaculation or nocturnal emission, testicular volume changes, or pubertal staging—each captures slightly different points in male maturation and produces inconsistent age estimates ^{[6] [4]}. Cultural factors affect reporting: embarrassment, differing sexual education, and recall bias skew retrospective data. Some reviews and clinical sources still cite older textbook ranges (boys 9–14 years for puberty onset) while more recent analyses cluster first ejaculation in early-to-mid teens, highlighting measurement and population differences as the main reasons estimates are not as tight as those for girls ^{[4] [8]}.

4. Putting male and female timelines together: ranges, overlaps and trends

When assembled, contemporary evidence indicates girls typically have menarche around ~12 years (recent U.S. cohorts ~11.9), whereas boys typically report first ejaculation around ~13–15 years, producing a modest age offset but substantial overlap ^{[2] [4] [7]}. Both sexes show trends toward earlier pubertal events over decades, but the female shift is better-documented with large population studies; male trends are suggested by smaller studies and clinical observation but are less precisely quantified ^{[1] [8]}. Genetic, nutritional, psychosocial and environmental exposures are consistently invoked as contributors to earlier timing, with rising BMI and possible endocrine-disrupting exposures recurring in recent analyses ^[2].

5. What the evidence does not settle—and practical takeaways

The data leave open key questions: the true global average for first ejaculation, how secular trends in boys compare across countries, and the precise causal mix behind earlier menarche. Existing work is limited by self-report, sample representativeness and changing diagnostic/measurement practices, especially for boys ^{[6] [7]}. Practically, clinicians and parents should expect considerable individual variation: most girls will begin menstruating around age 11–13, while most boys will first ejaculate in the early-to-mid teens. Public health attention should focus on monitoring trends, addressing disparities, and investigating modifiable factors such as childhood obesity and environmental exposures that appear linked to earlier puberty ^{[2] [3]}.