I knew it would happen someday, but not this soon.

I was in the checkout line at my favorite grocery with my nearly 3-year-old son, who loves to help put the food on the conveyor belt. He calls it "checking 'em out with the ladies," even if there's a guy ringing up our stuff.

The belt was broken so it made it harder for him to do his thing. I was having to move items toward the register.

The cashier looked at my son and out it came.

"That's nice of you, helping out your grandma."

I responded immediately.

"Uh, I'm mom."

To which she replied sheepishly, "Oh, I'm sorry." Then she said something about the sound of my voice but didn't finish the sentence.

I am 44. High school class of 1983. College grad from 1987. To figure out how old I was when I gave birth, do the math.

I felt compelled to explain to her in the time it took to ring up and bag our groceries, that yes I am older than the typical mother of preschoolers. But then as kind of a bragging point, I conceived at age 40 with no high tech fertility treatments. (The OB gave me a little low-dose Clomid just in case, but that side twinge I felt on alternate sides month after month made me believe it wasn't really necessary.)

I came to motherhood later in life, for reasons personal and mostly professional. I had heard the horror stories about "the mommy track" and I feared the points would change when I got pregnant. Then, at 39, I realized that all those co-workers and people I'd profiled probably wouldn't visit me in the nursing home or show up at my deathbed. But a child probably would, or at least the odds were better. (That's me with Dylan at right).

So my husband and I embarked on our journey to parenthood, which culminatined when I gave birth to our son three days after my 41st birthday.

Most of our contemporaries have tweens or teens, not preschoolers. But they aren't grandparents yet either. I figured I'd get the grandma remarks but they would come when I attended PTA or picked my son up from elementary school. I slather on sunscreen religiously, don't smoke and try to drink lots of water. I'm in good health. I also feel I'm better equipped now to have a child than I would have been in my 20s. We have a home that's not upside down, jobs, and most important, the patience and maturity that life experience brings.

So why is this insensitive remark about to set off a mid-life crisis? What should I have told the cashier? Would a snappy comeback have been better? I always think about those after it's too late.

Or should just remembering that a ton of 40-something professional women -- even the 60-something woman in Britain who recently became a mom -- are crowding into fertility clinics and being thankful that I wasn't one of them give me enough satisfaction?

Mommas, you tell me.

-- Lisa Buie, Times mom

[Top photo: Jupiterimages; bottom right: Lisa and her son Dylan]