Hair Foundation
HAIR LOSS » Hair Loss Causes
Male Pattern Balding

Male-pattern hair loss does not necessarily have a linear progression associated with age-that is, balding that begins as Type I at age 20 does not necessarily progress to Type VIII at age 45. Rather, androgenetic alopecia may progress slowly or rapidly and may or may not progress to a more severe stage. The pattern of progression may be somewhat predictable by patterns of hair loss in the individual's family; familial pattern is not completely reliable for predicting the eventual loss of hair.

From article:
Hair Loss and Its Causes