Cataracts. Cataracts typically develop with age.Generally cataracts can be detected by your eye doctor between ages 55-60, and then progress slowly and typically sugery is indicated 67-75 years of age. The development / progression of cataracts varies by individual. Cataracts can develop at any age, as well some live to be in their 90's (even 100) and surgery is not indicated.
Everyone's different. Cataracts always develop at different rates in different people. On top of that, the real issue is how they affect you on a day-to-day basis. This is because we don't talk about surgery until the cataracts affect your adl's (activities of daily living).
Long time. Depends on cause. Typical age related cataracts take years to develop (old age). Genetic related cataracts can occur at early age. Environmental acceleration of cataract formation such as uv light, radiation, steroid side effect, trauma, etc can make cataracts form very fast (even right away due to trauma) or months instead of years.