Andropause - Does it exist?
A. Koh
In a longitudinal follow-up study of 890 healthy men, the prevalence of hypogonadism as defined by a total testosterone of less than 11.3 nmol/L (325 ng/dL) increased with age from 12% in men in their 50s to 19%, 28% and 49% in men in their 60s, 70s and 80s respectively.
The Sigapore Family Physician April-June 2003

Prevalence, Diagnosis and Treatment of Hypogonadism in Primary Care Practice
C. C. Carson III
Hypogonadism affects an estimated 4 to 5 million men in the United States, and although it may occur in men at any age, low testosterone levels are especially common in older males. More than 60% of men over age 65 have free testosterone levels below the normal values of men aged 30 to 35. Studies suggest that hypogonadism in adult men is often underdiagnosed and under treated.
Boston Medical February 7, 2003

Fundamentals of Male Hypogonadism
A. M. Matsumoto
Approximately 20% of men in their 60s and approximately 50% of men in their 80s have serum total testosterone levels significantly below those ofyoung men.
Reviews in Urology 2003

Endocrinology of Aging in Males
I. Huhtaniemi
The prevalence of androgen deficiency (i.e. testosterone below 11 nmol/L) is 22% in men aged 60-80 years and 35% in men over 80 years.
International Society of Andrology December 21, 2002