Unfortunately, hair is not exempt from the physical changes that happen as you age -- it becomes drier, less lustrous, and for most of the population, gradual loss of pigment progresses from an occasional gray strand to a scattering of gray hairs throughout the scalp, culminating at some point into completely gray or white hair.
Usually, in a person’s thirties (or earlier, depending upon genetics or health factors), their melanocytes begin to slow down in their production of melanin. This typically occurs just in a few follicles and then gradually spreads throughout the scalp. Random hairs may become lighter and may not even be noticed, but eventually some begin to show as gray or white. This is much more noticeable in darker hair, so the perception is often that people with black hair go gray earlier, but that is probably not the case. As melanin particles disappear from the cortex, certain changes to the structure and properties of the hair can be expected. While people do experience their gray hair as being very similar to their pigmented hair, this is definitely not universally true. It is possible that those who had more highly pigmented hair to begin with (brunette, as opposed to blonde) will experience greater changes in the physical properties of their hair once those pigments are gone.