How soon can a man start to lose his hair?

Hair loss, or alopecia, can begin at virtually any age, though male pattern baldness — the most common type — usually begins in male adolescents and young adults. In females, it usually starts in the late 40s or early 50s, although it can begin at any age. While hair loss is most commonly associated with genetics and aging, it also might be caused by some medical conditions and treatments.