I am turning 40 this week. It's not all that bad. It's better than turning green, or turning sour. It's better than turning into a beetle.

With any luck, I will not wake up and find myself a metamorph. No Gregoria Samsa roles for me. I'm not up to overnight changes.

Though my friends and family have watched me for signs of imminent mid-life crisis, it seems equally unlikely that I will enter my 40s with a strong desire to sing at the Met or run a skin-diving operation in the Caribbean. I don't have the voice for one or the legs for the other.

But I will wake up irrefutably middle-aged.

By 40, the way I figure it, you have already created something unique: your life. You've created it with will and energy and accident.

Life begins at 40? Baloney.

At 20, I wanted to know who I would become. By 40, willy-nilly, ready or not, I've become. I have a web of commitments, a track record, a history. I've survived some things, hardened to some and opened up to others.

By now I have a context in which I live, a context in which to grow or a context out of which to break. Choose one of the above. I choose the first. c

Do I sound smug about it? Not at all. It's not that easy. I suffer from middle-age bulge. At 40, my life is inflated, like a tire, to the maximum of pressure. It comes with territory.

Middle age is responsible. Middle age is busy. Middle age is overcommitted. Middle age asked for it.

I spent my 20s and much of my 30s filling in the blanks, building a structure. It is the business of youth; it builds to avoid lonliness, uselessness, to test competence. One by one I got the basics: a career, friends, family. I have shored it up, renovated from time to time, but eventually I even added some frills: a house, a garden, commitments to causes and people.

All these things nourish and enrich my life. All these things require time, and attention. I spend less energy these days on construction and more on maintenance. I am conscious of the effort needed to keep it all together, in working order. I am conscious of the strength needed to hold it up.

The support system of my life requires, of course, support. So at middle age, my life expands with other people's needs.

Middle age has both aging parents and adolescent children. Middle age has bosses to please and deadlines to meet and bills to pay. Middle age sometimes feels useful, strong, sturdy and sometimes feels overwhelmed.

I look back over the caldendar of my week. Two columns, six dinner guests, a pair of new sneakers, a family conference, a dash from the plane to my daughter's concert, plus the usual. Some weeks I am amazed at how much has been accomplished. Other weeks I am enraged that my life can so easily become a list to be crossed off. w

I have, in short, all the pleasure and all the pressure of a full life. At the height of our dependability, mid-life bulges with the weight of our dependents.

Middle age also worries. It may be at work when an emergency comes up at home. It may be on deadline when a friend calls up with a problem. It may cancel dinner with mother because daughter needs time. It may have to cut short a weekend with family because a friend is in trouble. But it tries.

At 40, I am proud sometimes to be able to deal with all the aspects of my life without more than an occasional disaster. At 40, I am distressed sometimes by the idea that I am disappointing the people I love, unable to hear enough, be enough, do enough for them.

Still, like Popeye, I am what I am. Lucky. And rushed. Torn between people and warmed by them. Strung out between responsibilities and bolstered by them. I am in a pivotal and exhausting intersection of the life I willfully created.

And I know, without the shadow of a doubt, that these are my good old days.