It’s an age-related process but even juveniles and babies can develop cataracts at a much younger age. Probably 99% of cases are with patients over the age of 40.
Cataract is usually an ageing problem commonly presented in older patients. Some are born with congenital cataract and usually this is due to some disease. For example, the mother has chickenpox during pregnancy and this causes some lens proteins in the eye to become faulty.