Andropause, also known as male menopause, is the natural decline in testosterone levels that occurs in men as they age. It is a normal part of the aging process and is not considered to be a disease.
In most men, testosterone levels peak around the age of 20 and then start to decline. Most people do not notice symptoms associated with andropause until their 30s or 40s. Aside from age, testosterone levels can also decline due to medications and lifestyle choices.
An adult man's testosterone level should be between 270 and 1000. Testosterone levels peak at about the age of 20 years, and then the testosterone slowly declines with age. In younger men, the average testosterone level is in the range of 650.
A study from the Journal of Urology found the middle tertile testosterone level in healthy men to be the following:
20-24 Years of Age: 409-558 ng/dL (cutoff for low testosterone = 409)
25-29 Years of Age: 413-575 ng/dL (cutoff for low testosterone = 413)
30-34 Years of Age: 359-498 ng/dL (cutoff for low testosterone = 359)
35-39 Years of Age: 352-478 ng/dL (cutoff for low testosterone = 352)
40-44 Years of Age: 350-473 ng/dL (cutoff for low testosterone = 350)