It was at about 10pm last Saturday night, at my umpteenth wedding of the summer, that I really noticed the difference between the men and women in my early-30s friendship group.
On the dance floor, the blokes, downing shots of vodka, dancing sweatily, chasing the solitary single bridesmaid. Watching from afar, the girls - all engaged, married, pregnant or with children.
This gender divide has been sudden and extreme. At the age of 33, all of a sudden, most of the women in my circle of friends are "settling down". Meanwhile, the vast majority of the men are living lives that are no different from their 20s.
For our parents' generation, there was a widely accepted structure to middle-class life. You go to school, then university; you graduate, have fun in your 20s, then you meet someone; you buy a house, get married, have kids and live happily ever after. But for my generation, that's just not realistic any more.
For a start, we're far less financially stable - getting on the property ladder is by no means a given. We're living longer, too. On top of that, what is "normal" has changed. Our parents having a kid at 25 would have been considered par for the course. Now, if you announced you were having a baby at the same age, you'd be considered crazy.
The crucial difference between the sexes is that, while many women have an ominous voice in their head telling them to be mindful of that biological clock ticking down, men don't feel the same pressure. And that means we can find all manner of excuses to postpone having kids. "Plenty of time yet, I need to focus on my career for now, I want to be more financially secure."
Our female counterparts, meanwhile, are freezing their eggs in increasing numbers - spending what they imagined would be their baby-making years waiting for a man to be ready to take the leap.
Fertility experts confirmed this week what I already knew, warning that the demands of modern parenthood mean men are putting off children to avoid losing their free time, or compromising their careers.
In other words, now that couples increasingly share the burden when it comes to raising a family, men are recognising some of the pressures of juggling jobs with children. And we're making the choice to defer what many women would like to, but can't, as nature won't allow them to.
Because, let's be honest: having a child is a big commitment. And we men want to have our cake and eat it, too. Why wouldn't we want to prolong the hedonistic enjoyment of our 20s into our 30s - fuelled by a bigger salary? From a man's point of view, it's simple: when the big 4-0 starts to loom, then (and only then) do you need to start entertaining the idea of settling down, getting married and fatherhood.
There are many women who must feel the same - that 30 is too soon for them to be thinking about children. It's the age when careers are taking off, they're finally able to think about getting on the property ladder, and they're absolutely not ready for a baby. But they know they have a deadline, which men don't. Or at least that's what we're led to believe.
Most men (myself included) don't give their fertility a moment's thought until presented with evidence that there might be a problem. Mick Jagger can have a baby at 73, Robert De Niro at 68, we'll be fine. But perhaps we shouldn't be so complacent.
Modern life isn't necessarily conducive to strong fertility. Men's sperm counts in Western countries have been falling since 1973, with stress levels and increased exposure to chemicals and pesticides being blamed as the main culprits. Most men don't realise male factors are the cause of 40 per cent of couples' fertility difficulties, according to the British Fertility Society. Experts warned this week that so-called fertility boosters, which can be bought over the counter to improve sperm quality, do no such thing.
But online dating hasn't helped shatter the illusion that we can defer thoughts of fertility to our 40s. Now we can pick and choose who we meet, and how old they are. Most of my friends have their age range on Bumble and Tinder set to 24-28 years old: old enough to have stuff in common with, but young enough to not want a baby in the next five years.
Similarly, women I know who are looking to settle down are increasing their age parameters to 36-plus, to ensure they can get on with things if they do hit it off. It's a modern way of coupling up, and it certainly isn't helping to close that gap between what men and women typically want in their 30s.
As for me, my partner is my age - 33 - and yes, the biological clock is ticking. She wants a baby by 36, which means "trying" by 35, marriage by 34, proposal by... well, probably by the time I finish this article. Is that scary? Yes.
* As told to Eleanor Steafel.
The Daily Telegraph, London