Why did a 25 yr old from iran have a cataract?

Congenital: Usually congenital, either due to bad genes or infection in the womb. Trauma, iritis too. Those are the most common.

Many reasons: Reasons for cataracts in the young are traumatic (blunt, electric, chemical) congenital (galactosemia, rubella) , medications (radiation, steroids), diseases (diabetes, autoimmune, behcets, tuberculosis, glaucoma, uveitis). Too many to list. A cause should be sought and systemic associations evaluated.