I admit it, I sometimes forget Im not 21. Is that such a bad thing?

Recently I had my annual checkup with my primary care physician, and he asked dozens of questions to gauge how my health had changed in the past year.

How many hours of sleep do you get?
Seven or eight… but Im still recovering from the deficit I suffered during the first year of my 6-year-olds life.

Do you have any family members with a history of breast cancer?
Unfortunately, two.

When was your last period?
Two weeks ago.

How old are you?
Im uhhh …

That one should have been a no-brainer, and yet I found myself suddenly blanking on a number.

I hesitated not because Im ashamed of my age—which is, for the record, 36—but because I have a difficult time believing that I am, in fact, 36 years old. Whenever someone asks how old I am, my instinct is to say, "28."

Why 28? I got pregnant and had my son at 29. Every year since then has been a blur.

Even though my doctor told me that I could "totally pass" for 28 based on his evaluation, I wasnt sure I believed him. So I decided to get a more objective opinion by taking the Real Age Test on, which assesses whether you are "biologically younger, older, or the same as your calendar age." For 15 minutes, I answered a lengthy questionnaire about my health, habits, relationships, diet, and fitness with scrupulous honesty. Hey, Im pretty darn healthy, I thought. Maybe I can pass for 18!

Or not. My Real Age was 1.4 years older than my chronological age.

This miniscule gap—17 months!—between my chronological and Real Age bothered me far more than it should have. In fact, if Real Age had tacked on way too many years to my age, I could dismiss the whole thing as quackery. To come so close legitimized the diagnosis, so I took a serious look at the behaviors that added years to my life to see if I could do better.

One example: Real Age thought I should get a pet for companionship. (My charming husband and chatterbox son tried not to take it too personally.) But Im allergic to anything with fur and have a dismal history with suicidal goldfish. And speaking of fish, I apparently need to eat more of it, because Im not getting enough omega-3 fatty acids. Fine, Real Age. Ill buy more salmon. Could you please knock off those extra 17 months?

When I complained to my friends about "failing" the Real Age Test, they all said supportive things like, "Age is nothing but a number!" while also chiding me for being too honest.

"You should have lied," said my friend Eva, whose fibs resulted in a Real Age 12 years younger than her chronological age, a bogus result that actually inspired her to invest in music lessons instead of Botox. I laughed hard at that, which prompted her to ask, "Did it ask how many times you laugh every day? Youre always laughing and making people laugh. Thats a key to youth right there! Forget that extra 1.4 years! Youre a teenager!"

The impulse to lie about our age—if only to ourselves or (ahem!) an online questionnaire—reminds me of a T-shirt my Dad wore on his 60th birthday: Inside this shirt is an 18-year-old wondering what the hell happened. It seems that despite the evidence of our aging bodies, we all want to believe that we still resemble our younger selves. But the fact is, Im happy now. I wouldnt want to relive 18 or 28, even if it were possible. Its comforting to know that I can—on my best, laugh-out-loud days—still feel that way, though.