Me and my siblings all have a shared childhood memory – running to keep up with mum. She would storm through the underpasses, to the town, we'd chase her around the shops and then be begging her to slow down on the way home. The reason we'd stop at the bakery to get a cookie wasn't to keep us quiet, it was to give us enough energy for the journey back. It's one thing that me and my brothers have brought with us into our adult lives, double time walking as standard. Much to the dismay of my fiancée, she's a wanderer.

I've been spending more time at my parents' house in the last few months, usually with my Akita, Orla, in tow. I always make sure when I turn up to my folks' back door that I send Orla in first – the sound of her tapping along the laminate hallway is something my mum looks forward to now. For me, it acts as a buffer. I'm terrified of the day I walk through the back door and mum doesn't recognise me. As long as I hear mum say hello to Orla in the living room, I know that today won't be that day.

Mum's smile seems genuine when I mention going out for a walk with Orla at lunch time. We have the usual back and forth about where her coat is and that, yes, she probably will need it. Now, this is where I should explain a little bit more about Orla. She's a rescue, prior to me getting her she was significantly overweight, now she's just a bit overweight. Why am I telling you this? She's not the fastest of dogs. While most people who walk their dog have trouble with them pulling on the lead in front, I have a problem of Orla lagging so far behind her harness has been known to slip forward off her head. Years ago this would have been infuriating for mum, she would have hated having to slow down…or she wouldn't have done and she'd have left Orla and I languishing in her dust. It wasn't long after leaving the house and I noticed that when I looked over my shoulder to check on Orla, mum was a few paces behind me. She was looking at her feet while she walked. Disconnected. Oblivious to everything around her. I stopped to allow Orla to catch up, and when mum caught up with me she linked her arm through mine and without saying anything we walked on.

If you'd have asked me when I was nine years old, to draw someone in their sixties I'd have drawn an old person. Wrinkled, probably with a walking stick. Now I'm thirty, I see more sixty year olds in the gym than I do people my age. On a Thursday night at 7pm, the town running club convenes on the road outside my living room window and the average age there isn't far off sixty. Sixty isn't old. People are expected to work until they're nearly seventy, so why has my mum all of a sudden started acting like my drawings of a sixty year old? The truth is in the past few months I've really seen mum age. She's slower, she tripped on a walk, even making a coffee – it reminds me of being nine again watching my Nana standing in front of the kettle. If anything my Nana was quicker than my mum is now, but the wrinkled hands, weakly grasping the teaspoon…that's exactly the same. Yes, her dementia has progressed and ageing and dementia are socially synonymous. I don't know if in my head I'm conflating the two, whether, if mum didn't have a diagnosis I'd just be looking at a woman in her sixties, doing what she used to do but at 75% speed.

I'd love to think that's the case. But I don't think it is. What I'm seeing is a disease that's turning my mum into a stereotype of an elderly person before her time. We don't know at what speed mum's dementia is progressing, there isn't a one-size-fits-all scale that can tell us these things. But if I was to make a guess, she's ageing two years for every one currently, that's only going to get faster. Mum's only going to get slower. The coffee she brings to me in my office will take longer to make, if it gets made at all. Our lunchtime dog walks will become a gentle stroll, much to Orla's delight. The mum who would storm through the underpasses of Stevenage is gone. From now on it'll be me looking over my shoulder to make sure my mum is still there.