Sitting around the breakfast table, dad munching on his cornflakes, mum making toast, siblings arguing over the merits of muesli while you work your way through the bowl of porridge that is apparently 'good for you' - the only thing on your eight-year-old mind being what your school day has in store - is how many people spend their formative years.

Your parents become the soundtrack to your life, quick to reprimand your behaviour, ask you to eat things you dislike, and stop you going out when you want to or because you are wearing a skirt that they consider to be more like a belt. Imagine in little more than twenty years from that cosy breakfast scene that you could be censuring their behaviour, trying to stop them going out at all hours dressed in next to nothing, and only a few years later feeding them food that you have no idea if they will eat or spit out.

This is the ultimate role reversal, where you become the parent and your parent looks to you for the guidance they used to provide. It may sound like an extreme situation, but for hundreds of thousands of people this is becoming a reality, particularly as many couples are having their children later, and as those young people are busy growing up, the adults are heading towards health problems that could shatter their safe and secure family life.

In the most severe cases, this can mean early-onset dementia (defined as dementia in someone under 65). When dementia hits your family, the person with it develops that cocktail of vulnerability mixed with a need for independence that, in the early days at least, can be very similar to how that young person desperate to spread their wings might feel and behave.

It's often accompanied by denial on both sides, as the person with dementia tries to carry on 'life as normal' while their children are oblivious to the irreversible changes that are happening. I think most of us see our parents as frozen in time, a continuous rock in our lives, ignoring the ageing process and all its pitfalls.

We might leave home to go to university, hopefully then going on a career and maybe a relationship that keeps us many miles away from the parents we used to see every day. Meanwhile, if your mum or dad find that ageing brings with it mental or physical frailties that prevent life carrying on as it always has, you can be faced with the reality of putting your life on pause to parent your parent.

Nothing can really prepare you for that scenario. I was just 12 years old when my father began to exhibit the symptoms of what we discovered 10 years later was vascular dementia. My twenties weren't about university life, all-night parties and angst with boyfriends, they were about supporting my dad to have the best life he could, just as he had supported me as a child.

What surprised me is that rather than resenting my role, I actually grew into it. I learnt how to feed someone with a swallowing problem, knew all the words to the songs he loved, and became an expert at sewing name tapes into his clothes so they wouldn't go missing. I had become a parent and dad was, well, a 'new man' in every sense of the phrase!

Like every parent, I was told I was wrong on countless occasions, had to field numerous demands to know "Are we there yet?" and was asked for things I couldn't possibly provide. I would sign consent forms so that he could go on outings, was given paintings and crafts that he had created, and played endless guessing games when he was ill but couldn't tell us where it hurt. The difference between me and your average parent? 'He' was my dad.

From the ultimate role reversal, however, comes the ultimate lesson. Cherish every moment you have with your parents, however irritating, irrational or restrictive their parenting may seem. If you ever have to become their parent, you will understand where they were coming from. After all, the apple doesn't fall so very far from the tree.

Read more on dementia and ageing on Beth's D4Dementia blog: http://d4dementia.blogspot.co.uk/

Follow Beth Britton on Twitter: www.twitter.com/bethyb1886