When Testosterone Levels Peak in Men
Testosterone levels peak in early adulthood, specifically around age 19 years, reaching mean levels of 15.4 nmol/L (444 ng/dL), after which they decline to approximately 13.0 nmol/L (375 ng/dL) by age 40 years. 1
Peak Timing and Early Decline
Testosterone reaches its maximum at approximately 19 years of age, with mean levels of 15.4 nmol/L and a range (2.5-97.5 percentile) of 7.2-31.1 nmol/L 1
By age 18 years, testosterone has already peaked in healthy men, as demonstrated in Vietnamese population studies 2
The decline begins in the mid-30s and continues at an average rate of 1.6% per year thereafter 3
By age 40 years, mean testosterone falls to 13.0 nmol/L (6.6-25.3 nmol/L range), representing a decline from peak levels 1
Age-Specific Reference Ranges for Young Men
The traditional 300 ng/dL cutoff fails to account for age-related differences in young men. Age-specific middle tertile ranges for men aged 20-44 years are substantially higher than the conventional threshold: 4
- Ages 20-24 years: 409-558 ng/dL (middle tertile), with low testosterone defined as <409 ng/dL 4
- Ages 25-29 years: 413-575 ng/dL, with low testosterone <413 ng/dL 4
- Ages 30-34 years: 359-498 ng/dL, with low testosterone <359 ng/dL 4
- Ages 35-39 years: 352-478 ng/dL, with low testosterone <352 ng/dL 4
- Ages 40-44 years: 350-473 ng/dL, with low testosterone <350 ng/dL 4
Pattern After Age 40
After age 40 years, mean testosterone levels do not continue to decline significantly, but variance increases substantially. 1 This means:
- The average testosterone level remains relatively stable after age 40 1
- Individual variation becomes much wider, with some men maintaining high levels while others experience significant drops 1
- Free and bioavailable testosterone decline more steeply than total testosterone because sex hormone-binding globulin increases with age 5
Clinical Implications
The prevalence of low testosterone increases dramatically with age: approximately 20% in men older than 60 years, 30% in those older than 70 years, and 50% in those older than 80 years 3, 6
Important caveat: These age-related declines do not automatically warrant testing or treatment. Testing should only be performed in men with specific symptoms such as decreased libido, erectile dysfunction, or testicular atrophy—not based on age alone 6
Recent population trends show declining testosterone levels across all age groups when comparing recent decades (2011-2016) to earlier periods (1999-2000), even after controlling for body mass index 7