Male pattern baldness is the most common cause of hair loss
in men your age. Hair loss is genetically determined, but it may occur even if others in your family have not had hair loss, as the hair loss phenomenon may "skip" members of the family. The typical male hair loss pattern begins with thinning of the hair at the sides and receding of the hair line at the forehead. If your hair loss is following this pattern, then this is almost certainly what is going on.
Occasionally, there are other reversible medical problems that can be associated with hair loss. For example, it is important to make sure there is no inflammation of the skin of the scalp, which can cause hair loss. Also, certain hormonal conditions, especially an imbalance in the thyroid gland, can cause hair loss. Your doctor
may wish to perform some basic blood tests to look for any reversible cause of hair loss.
If this does turn out to be male pattern baldness, there are still medications that can be used to help thicken the hair and slow hair loss. In particular, prescription strengths of minoxidil (marketed over the counter as Rogaine) can be helpful.
Start by seeing your doctor for advice!