PARIS — IF all goes according to plan, I’ll turn 44 soon after this column appears. So far in my adult life, I’ve never managed to grasp a decade’s main point until long after it was over. It turns out that I wasn’t supposed to spend my 20s frantically looking for a husband; I should have been building my career and enjoying my last gasp of freedom. I then spent my 30s ruminating on grievances accumulated in my 20s.

This time around, I’d like to save time by figuring out the decade while I’m still in it. Entering middle age in Paris — the world’s epicenter of existentialism — isn’t terribly helpful. With their signature blend of subtlety and pessimism, the French carve up midlife into the “crisis of the 40s,” the “crisis of the 50s” and the “noonday demon” (described by one French writer as “when a man in his 50s falls in love with the babysitter”).

The modern 40s are so busy it’s hard to assess them. Researchers describe the new “rush hour of life,” when career and child-rearing peaks collide. Today’s 40ish professionals are the DITT generation: double income, toddler twins.

The existing literature treats the 40s as transitional. Victor Hugo supposedly called 40 “the old age of youth.” In Paris, it’s when waiters start calling you “Madame” without an ironic wink. The conventional wisdom is that you’re still reasonably young, but that everything is declining: health, fertility, the certainty that you will one day read “Hamlet” and know how to cook leeks. Among my peers there’s a now-or-never mood: We still have time for a second act, but we’d better get moving on it.