Today is my birthday. People are saying it’s a big one, although by nature every birthday is bigger than the last.

But yes, it’s one they print specific cards for (cards, not bus passes, just to clarify). One such greeting told me I’m now officially “over the hill”.

It’s been looming. I don’t know why the impending dread. It’s only a number after all. But it does seem to come laden with expectation. Forty just sounds so grown-up. It casts a harsh light on all my immaturity.

It also appears to be the starting gate for compliment qualifiers: “You’re looking good … for 40.” Wait, so how did I look for 39?

I don’t want to get labelled like that, boxed into an age bracket. We carry these pictures in our heads of what different numbers look like: how they should act, what’s appropriate, even what’s possible.

We’d better watch out because as we age we might start to believe them as true.

If you asked me as a child to do an impression of, say a 70-year-old, I’d have bent double, leaning on my imaginary cane, sucking my lips like I’d got no teeth. And 40, I’d have told you, was OLD; the start of that slippery slope down the “hill” I guess they’re referring to.

But what with advances in medicine and what we know now about health, diet, wellbeing (not to mention Botox), my version of 70 a generation ago isn’t even close to our actual potential.

We need to seriously update our pigeonholes otherwise we could be boxing ourselves out of our possibilities, stuck in our old ideas of numbers and the limited picture of what goes with them.

Check out the likes of Tao Porchon-Lynch, the 97-year-old yoga teacher, or Sister Madonna Buder, the octogenarian Ironman triathlete, for inspiration.

Iris Apfel, stylish mover and shaker, is still designing in her nineties. Allan Johnson is an 80-year-old rodeo rider, and Forrest Lunsway recently married his 90-year-old sweetheart on his 100th birthday. By these standards, 40 is the new 21.

Women’s ageing expert Christiane Northrup says not to celebrate the milestone birthdays, that defining ourselves by an age makes us feel that our time is limited and running out.

Instead, she suggests birthdays should be marked like this: “You celebrate everything that you’ve accomplished or that you’re proud of in the past year so that you have, really, a celebration of your worth and your increased competence. That’s a cool thing.” Agreed. Another year of experience, another year alive, is a badge of honour I’ll wear with pride.

Life is surely a series of peaks and valleys, a journey — not a “hill” you ever get over.

Let’s drop the numbers and the expectations. I have very little intention of growing up anytime soon. Today’s the youngest we’re ever going to be, so let’s party.

• Julia Pitt is a trained success coach and certified NLP practitioner on the team at Benedict Associates. For further information, contact Julia on 705-7488 or visit www.juliapittcoaching.com