It’s a natural occurrence, a natural degeneration of lens fibres. The other causes of cataract could be things like oral steroids, for example, if a person is taking oral steroids for a long time they do get cataracts.
Trauma as well, people who get injuries, be it sports or construction or accidents also get lens-related opacity related to trauma.
People with ocular inflammation uveitis or allergic conjunctivitis also get cataracts. So, most of these conditions can cause cataracts.