As a person ages, hormonal changes contribute to changes in the hair, the most noticeable changes are hair thinning, hair graying, and dryness of the hair and scalp.
Hair thinning in general is not noticeable in women until the mid to late twenties. With increasing age, the hair becomes thinner, what can lead to a perception of less hair volume.
The loss of pigmentation also turns the hair more prone to damage by sunlight exposure. Since the gray hair is lacking most of its natural protection (the melanin, that gives color to the hair), it will lose more protein and strength when exposed to sunlight. More details can be found on the article Hair melanin content and photodamage.
Dryness is another hair property associated with aging. With increasing age beyond the fourth decade, sebum output from scalp decreases, so the hair becomes drier, less soft and with less movement. The reduction in sebum output also can lead to a drier scalp.
Changes in the shape of hair also can happen with advancing age, what makes the hair more prone to frizziness and with less shine.
So, with advancing age the hair has different needs. When selecting products, it’s important to look for hair care products that will cover those needs, e.g. products that promotes an easier comb (since the gray hair is more prone to breakage), that will help to increase hair volume and body, increase manageability and decrease frizziness.
Hope that this information helps!