A physician said that cataracts have to be "ripe." what is he talking about?

Analogy: Trying to explain that all cataracts do not need to be removed, but they are typically slowly worsening over time. They can be observed until they are causing enough visual problems that removing them would make the vision significantly better -- thus "ripe" for removal.

Visual disability: The concept of a cataract needing to be ripe before removal is outdated. Ripe referred to how dense or cloudy a cataract appeared. Today, modern cataract surgeons judge a cataract by the visual disability they cause. A very early cataract with a central opacity can often cause glare and visual blurring that is more disabling then a dense cataract that in the past was classified as ripe.

Fruits ripe!: The olden days where a cataract had to physically harden to allow for easier surgical extraction with reduced complication are long gone! what is very pertinent here is that there is always a risk with any surgery. As such, unless the cataract is interfering with your vision, there is no need for surgical intervention.