• Tracey Kahn, a single mother by choice, gave birth at 49 and 51.
• The younger girl is a tween, and the older will turn 13 next spring.
• Kahn, 61, has found parenting more challenging as her daughters have grown older.

This as-told-to essay is based on a conversation with Tracey Kahn, 61, a publicist and the owner of a fine jewelry company in New York City. It has been edited for length and clarity.

I'd always thought that being a mom was part of my life plan. But it wasn't until my mid-40s that I began to wonder whether parenting would pass me by.

My career had always come first. Although I'd had serious relationships, I'd never committed to marriage. But, in the late 2000s, I thought, "Oh my God, I don't have kids!"

I'm a hustler and have always gone after what I wanted. I had a full physical and was approved for IVF using donor eggs and sperm. It wasn't the easiest pregnancy, but my daughter, Scarlett, arrived three days after my 49th birthday, weighing a healthy eight pounds.

I was keen for her to have a sibling. As soon as I felt my body had recovered from the C-section, I did another round of IVF. Scarlett's sister, Eloise, was born in December 2014.

Motherhood was exhilarating. I couldn't believe how lucky I was to have my own family at last.

Still, there were challenges. The worst thing was going straight into menopause the moment I stopped breastfeeding Eloise when she was 6 months old.

Raising my girls is more difficult at the moment

Despite the hot flashes and mood swings, I managed to keep up with the girls. There were times when I was exhausted because I constantly needed to catch up on my sleep. But, looking back, parenting a baby and a toddler was a cakewalk compared to raising a tween and soon-to-be teen.

The tougher years are going on right now. It's a combination of the girls approaching adolescence and me being in my 60s.

Scarlett is in seventh grade, and Eloise is in fourth grade. She'll be in middle school next year — the stage when children want their own identity and freedom.

It's certainly been the case with Scarlett, who turns 13 in the spring. She used to play with Eloise a lot, but she's now very sensitive and wants her own space and privacy.

I have to be thoughtful about how I speak to her because there's a lot going on emotionally. She's trying to find herself while dealing with school, friend groups, and boys.

When you're older, your short-term memory changes, but your long-term memory is very sharp. I remember sixth grade like it was yesterday. "It was the same when I was at school," I'll tell Scarlett when she talks about cliques. There's always going to be the geeks and the more popular kids.

But she doesn't like to listen to her mother, just like me at her age. She'll get mad and say that I'm too old to understand. We argue, and she calls me out on everything. I'm learning to back off and let her figure things out for herself.

I'm very aware of my advancing age

Meanwhile, managing the kids' activities is a full time job. Scarlett goes horseback riding and swims. Eloise plays lacrosse and volleyball. They love the arts. I'll take them to classes after school. They have sleepovers with friends.

It's non-stop. I constantly ask myself whether I can make it to another school function. I still want to enjoy things with my girls, but I'm slower than I used to be. I feel like I can't get out of bed sometimes because my joints hurt. I recently went to a field hockey game and met another woman my age watching her granddaughter play.

Late motherhood has made me hyper-aware of getting older. Scarlett has promised to visit my grave every day after I die. My sister said, "How can you talk about death like that?" But I find it endearing. It's better that the kids are realistic about the future.

People think it's morbid, but I have to think ahead. I'm a big planner and want everything set up for the girls in advance. I'll be in my 70s when they graduate from college. I don't know whether I'll be around to see them married. Then again, I could live to 95.

I cherish every moment

Eloise is such a sweet child, she gives me back massages at night. They're amazing. But I don't want her and Scarlett to feel I will use them as caretakers. I'll employ somebody to help me when the time comes so my daughters can travel and lead great lives.

In the meantime, I'm soaking up the joy of being with them. Every morning, I watch them go out the door to conquer the day. I'm excited to see them again at night. I want to know which poem Scarlett wrote and how Eloise did in her dance class.

You need perseverance to raise tweens and teens in your sixties. But the rewards are incredible.

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