Dear Grandparenting: I still have most of my marbles, make it a point to get 25 minutes of exercise daily, and read everything I get my hands on.

But a funny thing happened on the way to my 73rd birthday last Sunday. I forgot most of what I did during my 72th year, or my 71st to be honest. I don’t know where the years went. They seem to go by in a blink of the eye.

I say this because my five grandchildren were there for my 73rd birthday. I hadn’t seen my two grandsons living in San Diego in over four years. I well remember the last time I saw them. We played catch in their back yard with a toy football. Now they both play high school soccer and run track.

I was sort of stumped when my grandsons asked what I enjoyed most this past year. Nothing really stood out. I am lucky to have such fine grandchildren. Why in the world can’t I remember more to tell them? Mona Somerset, Fayetteville, North Carolina

Dear Mona: Childhood seems to roll out in slow motion, filling our memory banks with flashbacks and recollections. Moving through middle age, we begin to notice gaps in our ability to recall past events.

Then things start to go by more quickly. The passage of time accelerates and becomes blurred. Months and years meld together, creating imprecise sections of time in our memory during which nothing much seems to have much happened.

Here’s why: An event or activity is memorable to the degree it is new. You may never forget the first time you attended a major league baseball game, but the tenth game? And as we age, our memory banks become filled with a lifetime of experiences and facts, leaving less room for new entrants. There’s a limit to how much we can reasonably remember.

Scientists are unsure how the brain tracks time, but one fact stands out: Time exists as a byproduct of the events that occur within it.

Many grandparents follow a set daily routine. Maybe it’s golf and card games or gardening and reading, a way to pass time, not mark time. And that’s why grandparents who spend time with their grandchildren are rewarded with the gift of something to remember.

Grand remark of the week

Curt Williams from Fishkill, New York was catching up with grandson John, age 8.

“Salad is ruining my life,” declared John. “It kills my appetite just thinking about supper at home tonight.”

“Why’s that?” asked Curt.

“Salad is nothing but weeds. I don’t do weeds.”