Sitting in the middle rows of the Hollywood Cinema in Dereham a few weeks ago, watching what I have to confess is a hugely-disappointing re-working of the Dad's Army franchise, one of the scenes about halfway through was punctuated by the sound of a mobile phone going off.

There had been the polite on-screen plea, between the advertisements for cars and curry houses, to those in the audience to remember to switch off their phones so as not to spoil the viewing pleasure of other patrons.

That message, alas, had not registered with some, possibly too deeply engrossed in their barrel of popcorn or fizzy drink to notice.

It is not unusual for a phone to go off during a film or bleep with an incoming text, but what followed was a little surprising.

On and on the tones spilled out of the phone, as the owner fumbled in his pocket and then held it up to view the bright display and see who the incoming call was from.

'Hello,' bellowed the phone's owner. 'No, no, I can't really speak now, I'm watching a film.'

'Oh, Dad's Army,' in answer to the inquiry coming from the caller.

'No, it's a bit slow, but I'd better go.'

'Okay, I'll give you a call later,' said the man in his 70s.

'Bye, bye, yes, in about a couple of hours.'

It was as though Michael Gambon had clambered out of the screen and into the auditorium in the persona of Private Godfrey to conduct the conversation.

What made me think of the comic thoughtlessness of how this older individual had dealt with the unexpected incoming call was the recent suggestion by a large US cinema chain that it was considering letting customers use their mobile phones during some selected screenings.

AMC chief executive Adam Aron said – in a comment on which the chain later back-pedalled – he wanted to encourage what he described as 'millennials' to visit the cinema, saying: 'You can't tell a 22-year-old to turn off their cellphone.'

It wasn't so much the encouraging of the use of a mobile phone in a cinema that brought this to mind – though I believe that would be a bad step – but more the way it affirmed the assumption that it would be younger people who would use mobile phones in a thoughtless manner to the detriment of those around them.

And that is one of the difficulties in society, that we do make assumptions about young and old, about their behaviour, and pigeon-hole them without considering the broader facts, or the evidence staring us in the face.

We assume older people are polite and courteous, and younger people are more self-centred; that older people are cautious and considerate, that young people are perhaps a little more reckless.

Equally though, whenever there is a road accident involving an older driver, there is often this clamour for motorists of a certain age to be made to re-take tests whereas the evidence clearly shows that drivers at the highest risk of being involved in a road accident, or causing a crash, are the under-25s.

We are too quick to assume that young people will not be polite, thoughtful or considerate, but how wrong we are in that.

In the past in the cinema, going back to the 1970s and 1980s, the preview – or actually the intermission between the two films we used to get for our money – was punctuated by public information broadcasts; films about good manners, better driving, subtle messages on how to behave and treat fellow human beings or even tips on leading a healthier lifestyle.

The irony was that everything was filtered through the haze of cigarette smoke rising through the flickering light from the projector.

It is funny how the cascading ringtones of that Nokia phone in a cinema – in a movie that clearly had the older generation at heart as a target audience – provoked these thoughts about how young and old should view one another, and not make assumptions.

To me, that further underlined the importance of treating people as individuals, and not making knee-jerk assumptions and being drawn into forming poorly-informed stereotypical conclusions of one another.

Old and young have so much to give to one another, and respecting each other – whether in the cinema, the highway, the street or anywhere else for that matter – is a good starting point.