I have a birthday coming up soon, but it’s not my birthday I’m thinking of now, sleepless in the wee hours. It’s my husband’s. We share our birthday. Same day, different year.

Last year, I celebrated a milestone birthday. We’re skipping mine altogether next week. This year is all about him. It’s his turn for a milestone. (Sorry, Steve. You knew the risk when you married a writer.)

When we married later in life (in our 40s and 50s), I recited Robert Browning’s poem in my wedding vows:

Grow old along with me! The best is yet to be,

The last of life, for which the first was made:

Our times are in His hand, who saith “A whole I planned,

Youth shows but half; trust God: see all, nor be afraid!”

I changed it to “Grow older along with me” and we laughed; we didn’t feel the least bit old. Since that day, it feels like two minutes have passed, but the calendar tells me it’s going on 17 years. Now it’s not so funny. Now we stand on the threshold of old.

The question I’m pondering late at night is this: What exactly is old?

Whatever “old” is, it keeps moving. It’s always far beyond where I am. It’s beyond my husband’s age. Each time my next milestone rolls around, I’m so used to it, I might as well get on with it. I’ve lived with that age already for nine years. I’ve tried it on. I know how it feels, what to expect.

Not too long ago, Steve and I heard a doctor speak. He quoted a prayer of Moses from Psalm 90. “Our days may come to seventy years, or eighty, if our strength endures.” He said that even with all the medical advances, the average lifespan is still about the same as it was thousands of years ago. If we’re fortunate enough to reach 70 or 80 years, then anything else is just bonus. I turned to Steve and said, “I’m glad he’s not your doctor.” Then Steve laughed his hearty laugh out loud–and I mean loud–and I slid down in my seat and shushed him.

But I digress. There are a few things I’ve learned about age and getting older.

First, the number of years doesn’t matter at all.

Many people say what matters is your outlook on life. And I agree, to an extent. I know people my age who seem much older than I do, and also ones whose energy seems boundless, and I know there has to be more to it than how young you feel.

The verse I love to write in birthday greetings is one I’ve borrowed from a dear friend, inserting a couple words in brackets. “They seldom reflect on the [number of] days of their life, because God keeps them occupied with gladness of heart.” (Ecclesiastes 5:20)

Growing old gracefully is more than elasticity-laden skin, well-lubricated joints, or that elusive youthful attitude. It’s contentment with your life. What counts is the interior state of your heart. Peace that’s independent of circumstances–peace that I believe only comes from God.

Second, any birthday, but especially a milestone birthday, is a perfect opportunity for gratitude, reflection, and change.

Gratitude that you’re still alive. Thankfulness for the people who’ve touched your life, the opportunities you’ve had, the ways God has met you. All of it is a gift.

As you reflect on your life, consider if you’ve lived it well. Do you have any dreams unchased, opportunities left fallow, forgiveness to seek, relationships to mend?

If you feel a tug for a mid-course correction, do it. Now. If you need a fresh start, it’s never too late. You can make the changes that need making for your life to bring that gladness of heart.

Third, the one constant thing in your life is the one who formed you.

He was present at your birth, he’s been there every day since, and he’ll keep on carrying you until your last breath. Where does fear or dread about getting older fit with that?

“Listen to me … you whom I have upheld since your birth, and have carried since you were born. Even to your old age and gray hairs I am he, I am he who will sustain you. I have made you and I will carry you; I will sustain you and I will rescue you. (Isaiah 46:3-4)

The best part of birthdays? They’re a chance for friends to let you know how they feel. When you have a life rich in people, who cares what age you are?