Can only old people get cataracts? I'm 25 years old, and sometimes I can't see well because my vision is cloudy or I see double. Could I have cataracts?

Anyone can get them. Cataracts are a clouding of the crystalline lens in your eye. The most common reason for cataracts to form is age, however, people can be born with them, get them from trauma, or due to medications such as steroids. Cloudy or double vision can be due to cataract, but if it is intermittent, it is more likely due to dry eye, astigmatism, or another cause. Best way to know is a dilated eye exam.
Yes! At age 25 most likely not due to cataracts. It sounds like your symptoms come and go. You need an exam, but it sounds most likely that the surface of your eyes are drying, or you may need glasses for hyperopia.
It . It would be unusual for a 25 year-old patient to have cataracts. Previous eye trauma, or previous heavy use of steroids can cause cataracts at a young age. A comprehensive eye examination should reveal the cause of your cloudy vision.