I was on a train recently, and I was pleased to see that everyone was in a mask, including a quartet of boys aged around 13, sitting at a table and chatting.

They were obviously quite excited to be going for a day out in Norwich and were having a good time. but behaving perfectly well. However, as we drew into the station and the lads gathered their belongings and headed for the exit, a gentleman across the aisle caught my eye and muttered crossly: ‘Noisy, aren’t they?’

I was taken aback and said something meaningless like, ‘Well I’ve heard a lot worse.’ But then I thought about it and decided to add: ‘I know for a fact I was much noisier at their age! When you’re young you don’t realise, do you?’

He looked unconvinced.

I’ve thought about this a lot in the past week, and about how we have a tendency to become judgemental as we age.

And that led me onto thinking about how uncritical we often are of ourselves, and also about how we become set in our ways and our minds – and how very ageing that is.

My fellow passenger was probably around 65, and my guess is that he will go to his grave determinedly believing that most young people are loud and a bit of an inconvenience to himself. I think this is rather sad.

Lots of us have experience of parents and grandparents who grew repetitive and very stuck in the way they thought and behaved, and we vowed this would never happen to us.

After all, many of us who are now past the halfway point in our lives, grew up in the revolutionary times of the 60s and 70s when we threw out the old order, clothes and music, and rejoiced in living differently.

Did we think then that we’d become like our boring older relatives? Of course not. But it’s something that creeps up on us, alas, unless we make strenuous attempts to prevent it.

So, what can we do to keep younger in thought and action?

Probably the first thing is to avoid doing the same things in the same order all the time.

As we age, it’s easy to let our lives shrink. We drive less and when we do get in the car we tend to motor on the same routes and to the same destinations.

We often shop for the same foodstuffs week in week out and become quite limited in our choices. We may invariably go to the library on a certain day and meet a friend for coffee on another one and so on.

In other words, our routines become smaller, predictable, seriously unstimulating, and make us seem older than we are. If we want to change, we need to really shake this up and do something new.

It’s also important to eradicate phrases like: ‘As I always say…’ If you keep making the same pronouncements, there’s a strong possibility that your nearest and dearest are fed up to the back teeth with hearing them! So, if you catch yourself uttering these words, stop and change the subject.

Then I feel we should also challenge assumptions that we hold that are not only untrue but actually damage our health. One that I have heard a lot in consulting rooms over the years is: ‘It’s impossible to lose weight once you’re past 50’.

Now, we know that if we get toothache or a sore throat, we’re likely to lose a few pounds because it’s painful to eat and therefore we consume less. We also know that if we become badly distressed or heartbroken, weight often rolls off us.

So, actually it is always possible to lose weight – even if it’s hard. And we should galvanise ourselves into doing it if we know that those extra pounds are endangering our fitness and longevity.

It’s also important to stop saying: ‘I’m too long in the tooth to learn about computers.’ Or: ‘I’m too old to change my ways now.’ This is nonsense.

Unless we are cognitively impaired with some sort of dementia, we have brains capable of forming new connections right up till the day we die. So, we can always learn new things, and we should, even if it takes longer than it used to. Encouraging our brains to work harder is one of the best anti-ageing tactics there are.

So, make a conscious decision to open yourself to new thoughts and new actions.

It will get you out of a rut and encourage better mental health.

Watch a TV documentary you know nothing about. Make a habit of talking to someone new every day. Walk to the shops a different way from usual. Eat something you’ve never cooked before. Try doing a household task with your less dominant hand – like the ironing. All these activities can help keep our minds more flexible and more enquiring. And when that happens, we grow old less quickly.

It’s an effort to stay young in mind and body. But if we don’t want to be repetitious, boring, set in our ways, and rigid in our thinking, it’s an effort worth making.