"I love my mother—she is 50 years old, by the way—very much." This remarkably High German–inflected message was written by my 9-year-old son in an e-mail to a friend. His friend's mother e-mailed it back to me so that we adults could laugh together. So she laughed with me and I laughed with her and no one "laughed at"—as we always tell the children—although, at a mere 37, she did laugh longer.

My son, on the other hand, rarely misses an opportunity to rub it in. I am the oldest of the mothers among his classmates, and this has turned me into some sort of weird math problem. "If you add my age and Byron's age and Callan's age and Alex's age and Sam's age, you still wouldn't have 50." Or: "If years were liters and you subtracted Mona's mother's age from my mother's age, you could fill two 10-liter buckets." Or: "Fifty years is half a century. Can you figure out how many centuries 50 times 40 times 30 times 20 times 10 is?" At last I understand why women of my mother's generation kept their age to themselves. It wasn't vanity; it was self-defense.

I've been lucky, I suppose. I've never been saddled with angst about milestones. At 30, I was an up-and-coming career woman and so well established that I'd stopped worrying about not being married. At 40, when women get anxious about their biological clock, I was so happy and confident about life that I decided to spread my good fortune by adopting a child as a single parent. At 49¾, I was a passionate civil rights advocate, productive in my career as teacher, lawyer, writer, and mother to a child whose every tic and gesture filled me with delight.

On the morning of my 50th birthday, however, I woke up feeling odd. I did not leap out of bed with a glad spring to my step, because my heart was fluttering, my bones ached, and my back hurt as though I had run a marathon—which I had not done, but which I keep meaning to do, maybe one day after I finish making dinner and doing the laundry.

Before noon I had suffered what I thought was a massive coronary occlusion, but which my doctor classified as a mild panic attack. She recommended green tea and yoga, an idea I have every intention of exploring right after I run that marathon. By midafternoon, I discovered that my eyebrows were graying—as was my complexion. I had to comfort myself at once with a large box of birthday eclairs, and by the end of the day, mirabile dictu, I had put on 20 pounds. Just like that.

The point is, at 50, I realized I had to get my life in order. So I drew up a protocol for eating right and getting plenty of exercise. I used up a whole pad of paper that had come with ROOM FOR IMPROVEMENT printed across the top of each and every page. I bought jogging shorts with a drawstring waist, imagining drawing it steadily inward over time.

But ten months later, the only real change in my life is that I started piano lessons. Don't ask me why. Perhaps because I could do it sitting down. But maybe it's also that, even more than whipping myself into shape, I realized I needed just one activity that involved no whipping at all. Music was not a predictable outcome of my midlife crisis, although I had, at least, learned to read notes in my childhood. My mother played cello with the Civic Symphony in Boston; she was an ambitious mother, so I began music lessons when very young. To utterly no avail. I have pictures of me holding my quarter-size cello, looking pint-size and precocious, but I never came close to living up to the image. Indeed, it was a music teacher who suggested that my playing indicated great promise as a lawyer.

I did buy a piano when my son was born, not for me, but as some remnant of my mother's ambition. When he was four, I enrolled him in Suzuki piano classes, where he spent a great deal of time rolling on the floor and groaning. Luckily for him, a friend gave him a trombone two years ago, an instrument he loves and with which he bargained his release from the hated piano. But it was at that point I realized that if I'd never liked the cello, I'd always loved the piano.

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