If someone has cataracts how quickly does he need cataract surgery?

Depends. Once the cataracts are "visually significant", i.e., your vison can no longer be improved with glasses or contacts then it's time to consider surgery to remove them. Most patients will begin to notice significant "glare" with oncoming headlights or even avoid driving at night. Talk to your eye surgeon. He or she can give you an idea of how advanced your cataracts are and a timeline on eye surgery.
Progression depends. Not all cataracts require surgery. If best vision is worse than 20/40 or glare is significantly affecting VA, most surgeons prefer to do surgery sooner but depends on pt's sx, risk factors, pt's preferences; also, though no guarantees with any surgery, many patients are less dependent on glasses & even glasses free after surgery which helps many in decision process; info: eyedoc2020.blogspot. Com.
Cataract surgery. The decision on when to proceed with surgery depends on the patient's best corrected vision and its impact on their normal daily activities. Once the cataract is limiting vision and their activities, surgery can be considered.
Symptoms. When the symptoms affect your activities of daily living or what you like doing.