Hair loss in men is likely to occur at any point between late teenage years and age 40-50. In general, those who begin losing hair in the second decade are more likely to experience severe hair loss. In some men, initial male-pattern hair loss may be delayed until the late third to fourth decade.
There are several types of male and female alopecia. Androgenetic alopecia is an extremely common disorder that affects roughly 50% of men and perhaps as many women above the age of 40 years. Reportedly, as many as 13% of premenopausal women experience androgenetic alopecia.