In my early 20s, my personal fitness landscape was so vastly different to what it looks like now in my mid-thirties, it might well have been Mars.
While the memory is a bit fuzzy from too many rum-related hangovers, I'm fairly sure my daily diet consisted of chips and a saveloy, and exercise consisted of walking to the shop to get my chips and saveloy.
My body was also at the peak of its tolerance for eating crap and being sedentary, which meant that although I did zero exercise and ate terrible food, I didn't really put on weight.
That swiftly changed in my late twenties, and now in my thirties, I am a lot more clued up about nutrition and fitness. Mainly because I've found out the hard way how a chips and saveloy diet affects the waistline and also because getting strong, to me, is much more satisfying than hitting the pub every night.
Fast forward to present day. A catalogue from one of my favourite fitness brands pops through my letterbox - it's a guilty pleasure but I love rooting through it to eyeball the latest fitness kit.
But - call it turning 35 - this time round I notice just how young the models are. I mean - they aren't even within a decade of my own age.
Then I go online and I see this standard of fitness and beauty replicated across almost every single major fitness brand.
There's no hating on the models here - fitness models look lean, healthy and toned, which is more than can be said for some fashion models. But part of me was actually put off from making a purchase - mainly by the brand's vision of what they think is aspirational and will get me to buy their clothes.
Because Back To The Future is a fictional film, and no one has actually invented a time machine, there is nothing fitspirational to me about a 20-year-old. It's something that is physically impossible to aspire to: I can't turn back the clock and no amount of lycra is going to restore the luminescence of my youth.
It may not be the most elegant way of framing it, but it makes me feel shit.
Not speaking directly to the 30s and 40s female market seems like a big own-goal for fitness brands because:
1) I'm far more likely to spend more on fitness gear in my 30s (and 40s) than I ever did in my 20s. Not only do I earn more than I did at 21, but I prioritise fitness in my life. As such, I want to look good when I am doing it.
My first gym outfit, when I was 23, consisted of a pair of jogging bottoms I bought from Primark for £1, and a free baggy t-shirt from Lambeth council.
I may have looked like a bag lady, but there was no way in hell I was going to spend my meagre, precious salary on a £30 vest or £70 leggings.
2) While I think young models are a critical part of inspiring younger women to exercise, I think the same could be said of including a more diverse age range.
Having been a 20-something, I know that being in shape is something that comes more naturally and easily than it ever will at any other age.
As such, when I'm scrolling through the news for fitness inspiration, the stories I am most likely to read are of the women who are doing amazing things in their 30s or 40s, or the Instagram fitness success stories that reveal vulnerability but also great strength.
This constant sense of striving, of being able to better yourself no matter what age is what fuels my motivation and desire to keep fit. The same works for the brands that are selling to me.
3) Fashion was much braver with age in 2015 - from Joan Didion for Céline or Joni Mitchell for Yves Saint Laurent - and the reaction was overwhelmingly positive.
Women are fed up with being sold perfection. We're fed up with running on a hamster wheel to nowhere, striving for something we're not quite sure we want or will ever attain. We're far more likely to cough up our pennies for something that resonates with us emotionally.
It doesn't mean that I won't buy something if the model is young, but I'm far more likely to make an emotional connection and keep coming back if I see something I can relate to.
The other day I bought something from Fabletics purely because Kate Hudson (36 and counting) was the one flogging the kit.
So get with the times and start trawling Instagram for these amazing, older women who are doing incredible things with their bodies. Because fitness certainly isn't the preserve of the young, so let's see that reflected in the way you sell them to us.
Follow Poorna Bell on Twitter: www.twitter.com/HuffPostPoorna