How do average penis sizes vary by age group across adulthood?

1. Growth curve: When most penis development happens

Medical reviews say penis growth occurs in two main windows: an early phase between infancy and about age five, and the second phase beginning about one year after puberty starts and finishing usually by about 17 years old — meaning most size variation is set by late adolescence ^[1]. Parent-facing guides and sexual-health summaries echo that puberty (driven by testosterone) is the period of rapid change and that growth generally stabilizes by early adulthood ^{[5] [6]}.

2. Adult averages: What studies report for erect length

Large clinical syntheses and mainstream health outlets converge on an average erect length near 13 cm (roughly 5.1 inches). A 2015 health-profession-measured systematic review cited an average erect length of 13.12 cm (5.17 in) with an average girth of about 11.66 cm ^[1]. Other summary sites and data projects report a typical overall range between ~12.9 cm and ~13.9 cm as a reasonable population mean ^{[3] [2]}.

3. Variation by age in adulthood: Little consistent age decline in the literature

Several overviews and data compilations note that age by itself has not been reliably correlated with smaller penis size in adulthood; many studies find negligible effects of age on hard measurements ^{[1] [7]}. Sources do cite that after stabilizing post‑puberty, average measurements remain broadly similar across adult decades unless confounded by specific health or body-composition changes ^{[1] [4]}.

4. Factors that can change “apparent” size in adulthood

While chronological age alone is not strongly linked to shrinking, factors that become more common with age — especially obesity (increased pubic fat pad), certain illnesses, low testosterone, and some surgeries — can make the penis look shorter or affect erectile function ^[4]. Medical sources discuss “apparent” length loss due to fat accumulation at the pubic bone and note that obesity and some health conditions can affect penile appearance and function ^[4].

5. Measurement issues and self-report bias

Research emphasizes measurement method matters: studies where clinicians measured participants report lower averages than self-reported surveys, and men tend to overestimate their size when self-reporting ^{[1] [2]}. Flaccid length is a poor predictor of erect length; “growers” and “showers” differ in how much length increases with erection, which complicates comparing across age groups without standardized protocols ^{[1] [6]}.

6. What the consumer-facing guides add — and their limitations

Several consumer and clinic blogs present age-by-age charts and give granular numbers by decade, but these often mix self-reported data, extrapolations, and commercial aims (e.g., offering interventions), so their figures should be treated cautiously ^{[8] [9] [4]}. Wikipedia and major medical summaries focused on peer-reviewed syntheses provide more conservative, methodology-aware figures ^{[1] [2]}.

7. Takeaway for readers worried about size and aging

Available reporting indicates your adult erect length is largely determined by adolescence, and there is no strong, consistent evidence that normal aging alone causes a systematic shrinkage in measured penis length ^[1]. However, weight gain, hormonal changes, and health problems that become more common with age can change the penis’s appearance or erectile performance, so addressing general health is the most evidence-backed route to preserving penile appearance and function ^[4].

Limitations and gaps: None of the provided sources offer a comprehensive, peer‑reviewed chart that breaks average erect length by narrow adult age bands (e.g., 20s vs 30s vs 40s) with standardized clinician measurements; where such breakdowns appear in consumer pieces, methodology and possible commercial bias reduce their reliability ^{[8] [9] [4]}. Available sources do not mention precise decade-by-decade clinical averages across adulthood in a single, standardized dataset (not found in current reporting).