As I dropped off my five-year-old son at the kids' birthday party venue I introduced myself to his friends' mum for the first time. "I'm his father!" I said loudly.
It may sound like I was stating the bleeding obvious but I wanted there to be no doubt that I was not some middle aged relative standing in for his older parent.
With my grey bushy beard, bulging belly and careworn face I'm pushing mid 40s. And having been mistaken as my son's grandfather before, I'm now determined to make sure I save everyone embarrassment from the outset.
My wife gave birth to our first child when I was in my late 30s. I was more than 40 when our second child arrived.
OK, so I may not be exactly ancient, but I was five years older than the current national average for a first time father. And I can certainly tell that, when I'm in a group of dads with children the same age, I tend to be the oldest – as well as the most knackered looking.
When I referred to having done O-levels to one fellow father at the school gates he looked at me a if I was something out of the Ark. I recently went out with some of the dads from the National Childbirth Trust group that we joined when my son was born. One of them was having a meltdown about his 'big' birthday coming up and was worried that, because he had started listening to Radio 2 rather than Radio 1, he must be 'getting old'.
When it turned out that he was panicking about turning 30 I had to laugh.
Yet, on the way home, I began to start worrying that I had been selfish by leaving it late. The truth is that I had been having way too much fun in my 20s and early 30s to think about having kids and, until we actually had them, I hadn't fully considered how having children later in life would impact or them or me.
I certainly hadn't given enough thought to my expanding waist or the physical demands of having children.
Am I letting my children down by running the chance of dying when they are still relatively young?
While my own parents are still spritely what are the chances of me being around for long enough to help out with my grandchildren as they have done with theirs?
When it comes to worrying about all this I know I'm not alone - these days two thirds of new dads are over 30. Back in 1971 the average age of a new father was 27. By 2065 experts say the age of a first time dad will be 40!
Of course, for some dads the issue of age is much more pressing than for me. I know of another dad who has a child under 10 who is 60. He hasn't even told his own son exactly how old he is yet for fear that his school friends will tease him.
Just imagine how the world's oldest father, Ramajit Raghav, from India feels. He became a father for the first time in 2010 at the age of 94.
Among the factors that are making dads wait to have children is the increasing financial pressure of having a family. Of course there's also opportunity – we don't have quite the same issues with biological clocks stopping us from reproducing.
But leaving it until you're older might be detrimental to your child. A host of studies has shown that the babies of older men are already at greater risk of autism, bipolar disorder, low IQ and schizophrenia. While scientists from Liverpool John Moores University have found that older males tend to produce smaller and unhealthier children than their younger counterparts.
Apparently it's all to do with the quality of sperm!
There's even research to show that the kids of older dads are less attractive. Though, of course, I'd have to disagree with that one.
On a more practical note it may not be long before my eldest son can run faster than me! More importantly will he be mortified when he finds out that I can't run faster than any of his friends' dads come this year's father's race on school sports day?
Yet I've concluded that there may be some positive things about being an older dad. I'm certainly more emotionally mature than I would have been as a father in my 20s. I'm more financially stable and less career obsessed.
Plus, well, dammit, I know more stuff. Not just facts to help answer those tricky questions my sons fire at me every day, but about life and how to deal with the problems it throws up.
Even my lack of energy can be a benefit. It means we're actually better matched when it comes to playing football – I don't need to 'pretend' so much like those super-fit young dads do.
Perhaps the biggest benefit of all is that as you get older you tend to treasure the important things in life a little bit more. And when it comes to having children I'm so glad I got round to seeing what all the fuss was about – eventually.