I have 12 days left in my 30s.

I’ve noticed that a common response when confronted with the fact of aging is to say, “I don’t feel 40!” “I don’t feel like I’m 65, I still feel like a teenager.” I guess I can understand that. Whatever our age, our sense of self — dare I say soul — remains constant, ever as present and weighty as the year before.

That said, in 12 days, I won’t be proclaiming that I don’t feel 40. The truth is, I do. My 30s have been a decade-long realization that, physically, I no longer enjoy the invulnerability of youth. I don’t bounce back from injuries as fast. I seem to fall out of shape more easily, and I struggle more mightily to regain some semblance of form. I avoid sports that I formerly dove into with abandon. Now, I think, “That would probably hurt.” More than invulnerability, I simply wish I could again feel that surge of strength and energy that, in my younger years, I simply took for granted. I believe I’m about to lapse into an infomercial for testosterone, but opening the childproof seal on the ibuprofen bottle is clear and convincing evidence for me that “she ain’t what she used to be.”

And it’s not just in my head. In the morning, I look into the mirror to see post-surgery scars cover my right shoulder, and, as I lean in to examine them more closely, I’m reminded that my right knee was reconstructed with the help of four titanium screws. Sure, I still run miles every week, but only with the arch-supporting aid of orthotics. Moreover, as the air whips through my hair, it stays anchored with the aid of hair loss medication that I dutifully quarter and take every morning. And that’s after I lather my skin with lotion, given that time has robbed me of adequate dermal moisture.

No one ever said aging was pretty.

All that said, when February 28 comes around, I won’t be sad. I won’t pretend like I’m not a year older. I will be. I’ll be 40. I’ll embrace it, love it even. For all the aches and pain that will surely only accumulate as the years tumble on, I wouldn’t trade where I am now. Sure, maybe I’d love my 20-year-old body and the keenness of my 30-year-old mind, but I’ll take the whole package at 40. I think I’m getting the wiser part of “older and wiser,” even if I’m taking my own sweet time.

I’ve lost that invulnerability, that feeling that I can do anything, be anything, conquer it all. Life’s lumps have a way of humbling you. The daydreams of setting the world on fire are fewer and far between now, replaced by the growing understanding and acceptance of my insignificance. Not a melancholy insignificance, but a properly respected appreciation of the order of the cosmos, the way of things, a right-sized smallness in an awe-inspiring world. There’s a peace in that; delusions of greatness are, after all, quite the burden.

Lately, on many evenings, as I sit by the fire and read a good book, I’ll look up to see my husband reading too or toiling away on his laptop. It will be warm and quiet and peaceful. I’ll think about all of our adventures, and I think about the even more exciting exploits that lie ahead. I’ll consider the green stuffed monkey waiting on our bureau, and the trips to new places, and the comforting expanse of an unknown destination called life, and I know that this is a good place, this is where I was meant to be. It’s the moment to understand that what you’ve gained mightily outweighs what you’ve lost.

This is 40, and it’s worth the aches and pains.