When we are born our natural lens in our eyes are clear like a new pair of glasses. Then over time that lens begins to become cloudy or foggy. That is when we call the natural lens a cataract. At about 50 years old there will be mild signs of cataracts. The first and most common symptoms is sensitivity to glare at night. At about the ages of 70-80 most people will have a visually significant cataracts and surgical intervention would be necessary for improved vision.
Other factors can accelerate the development of cataracts like if a person is taking an oral steroid for long period of time, if a person is diabetic and or a person who is exposed to a lot of UV rays.