As my twin granddaughters turn 15, they are fearless. But I see time’s passage very clearly

In the blink of an eye, the bald, bawling babies I once soothed are now in high school.

In the blink of an eye, the toddlers who played musical chairs at birthday parties now practice the viola and paint on canvas.

In the blink of an eye, the same little girls who drove a pink Barbie jeep around my yard are learning to drive with their father.

Sometimes I don’t believe it. How did this happen so quickly? Can’t we slow the clock for just a bit, at least until I catch my breath and calm my heart?

There is nothing quite like a grandchild’s milestone birthday to remind you of the speed of time — or to underscore what my father often said, El calendario no perdona .It was his way of emphasizing how, in spite of our best intentions, we all inevitably get older.

My twin granddaughters turned 15 earlier this month, and that has forced me to pause and reconsider how I’m using the days and months left to me. Adjusting my priorities has never come easy. I dash from day to day, meeting deadlines and checking off items on my to-do list, but rarely stop to glance ahead or look back. In other words, I’m good at seeing the trunk of trees but never the expanse of forest.

Their special birthday stopped me in my tracks. The celebration — not the traditional quinceañera but a family dinner at a Korean barbecue restaurant — came at the tail end of a trip that began in another city to welcome my youngest grandchild. These two momentous events bookended a three-week period filled with joy, to be sure, but also threaded with the bittersweet undertone of nostalgia.

I love the young women they have become, so generous and witty and conscientious, but I also miss the children they once were. Even as I swell with pride, I miss the lap time, the hand-holding, the cuddles, the very physicality that marks childhood. That’s not to say they’re not affectionate, because they are and they dispense hugs easily, but it’s not the same. I don’t mean worse or better, just different.

And for an abuela, that difference can require an adjustment of both perception and behavior.

Another thing: As they march fearlessly into their future, debating majors and colleges and extracurricular activities, I feel the limits of my own. Their lens is wide and expanding, as it should be, but mine turns increasingly inward. I think this is an unavoidable factor of age and experience, a recognition of mortality.

During our visit, the twins’ father, my eldest son, confessed that he had sailed through his 40th birthday, with hardly a look back. Sure, there had been previous brushes with the inexorable march of time — the start of middle school, the first driving lesson, the gray in his beard — but the Big One-Five, that did it for him.

The twins introduced me to the exalted state of grandparenting and, by the very nature of being first, they have therefore served as ambassadors to every landmark of that adventure. When they were born, a much older friend explained that inaugural grandchildren serve as guides to our new roles.

She was right. From them I’ve learned so much about how to act with children who aren’t my own but feel like they are. Their cousins, I think, have benefited.

Days before the twins’ big birthday, a dear friend became a grandmother herself, a role she had silently coveted for a while. Pictures of her holding the baby showed a woman elated by the tangible reality of the next generation, by a living legacy like no other. Her grin was a mile wide.

I know exactly why she was smiling so generously.

Ana Veciana-Suarez writes about family and social issues. Email her at avecianasuarez@gmail.com or visit her website anavecianasuarez.com. Follow @AnaVeciana.