The adage most appropriate to memory function and aging is

"use it or lose it"

Explanation:

"Use it or lose it" is a principle that applies to the function of the human memory, which emphasizes that for our cognitive ability not to decline or be strengthen over time, the brain must be kept in constant use.

It is said that as one ages, if one does not remain mentally active by engaging in activities and tasks that ensures stimulation of the brain, one's cognitive ability is likely to decline. This is why the adage "use it or lose it" is often used to describe this particular memory function as it relates to aging. Aging adults are being advised to engage in mentally stimulating activities upon retirement, in order to prevent impairment of memory function. The brain should be exercise to keep it functioning properly.

The correct answer to this open question is the following.

The adage most appropriate to memory function and aging is "use or lose it."

That is why it is so important to continually exercise the memory function so the brain never loses its ability to do something previously learned. You use it and you practice it so you master. Mastery is the result of constant repetition. So it is better to use something to be fresh in the memory and could be used when needing it.