On average, a hair grows for 3 to 6 years. Average hair grows about half an inch each month during that time, but at the temples, it tends to grow a bit more slowly. After this time, it slows its growth for a few weeks, then rests for a few weeks before being shed. There are always people whose hair will grow longer than 3-6 years or for less time than that. Variation is normal, of course! Hair on the legs and in the armpits grows at a similar rate to scalp hair.
Does your hair have an average, above average, or less than average life-cycle?