Hair grows all over your body except palm of your hands and sole of your feet. Some hair is visible but some are so fine, so hardly visible.
90 percent of your hair follows a two to six year growth cycle. This is known as Anagen phase of hair growth. The balance 10 percent is in a two to three month resting phase known as Telogen. After the rest period, it sheds and new hair starting to grow. The loss of hair could be of 80 to 150 hairs a day based on your age, hair type, decease, and other genetic conditions. Hair can grow up to six inches a year. But as you age, growth rate of your hair is slowing.
So, gradual thinning of your hair with age is natural. More and more hair goes into Telogen phase with age. However, males can experience thinning of hair as early as their teens or twenties, while women may experience this in their 40s. This condition is known as Androgenic alopecia (for men it is commonly known as Male Pattern Baldness and for women it is Female Pattern Baldness). If you experience non age related condition, seek help from a professional.