For 57+ f, should cataract be operated as soon as it's detected ? or, should it wait until being necessary ?

Only when needed: Cataract at any age should be removed only if there is likelihood that vision achieved with surgery will offer a benefit over what it is before surgery. Typically, early cataracts can be watched for some time before surgery is necessary.

It is your decision: I would suggest removing the cataract when the vision is decreased to a level that is interfering with your life style. If it not bothering you there is no reason to do anything about it.

When necessary: Cataract surgery is highly successful. I tell my patients that the time to get it done is when visual activities and tasks in your life become difficult. You don't want to wait until they become impossible. It can take years for a cataract to get to visual significance and the mere presence of a detectable cataract is not the time for surgery.