This week I was in the car with Molly. It’s always a good chance to spend some time with her and we started chatting about elderly friends and relatives. She was obviously wondering from the bounciness of youth what it’s like to be old and she asked me what initially seemed like a simple question. ‘Mum,’ she said curiously, ‘Do you feel like you’ve lived a long time?’

This was surprisingly hard to answer. My first reaction was to say, ‘No,’ but that seemed silly as I evidently have lived for quite a long time. Then I realised that this kneejerk feeling comes from the fact that for much of the time, I don’t feel properly grown-up. In my head I’m still waiting to get to that elusive state.

I clearly have a problem as I read recently that a life insurance provider asked 2,000 people to say what they thought marked the transition into adulthood. The most common answers were buying a first home, becoming a parent and getting married. Other signs of being grown up were paying into a pension, becoming house proud, taking out life insurance, looking forward to a night in, doing DIY, hosting dinner parties, and having a joint bank account. I’m 56 and I’ve done all of these things (with varying degrees of enthusiasm)—but I still keep expecting to be outed as a pretend grown up.

I think that much of my grownupness deficit comes from being a younger sibling. My beloved sister is twelve and a half years older than me, and when, aged twenty-eight and four years married, I told her that I was pregnant, she was noticeably shocked. ‘Do you feel grown up?’ I asked her once. ‘Of course I do,’ she said, briskly.

As time passes, I suppose the reality is that I do get more practice at being grown up, like when Molly was seriously ill, earlier this year. I felt pretty adult then. This, and other snapshot moments force me to adjust my internal age-barometer. But it’s a jolty kind of process rather than a continuous smooth one. A recent blow was discovering that the actor George Cole was 90, when he died, this year. ‘He can’t have been,’ I thought. However, if he was a great deal older than when he played Arthur Daley in ‘Minder’, then the inescapable truth is that I’ve got a great deal older, too.

Some of the most poignant age-related jolts come from reflecting on missed opportunities. I feel sad when I recall things I planned to do with the children but didn’t get around to: I never took them to see a ballet; I got stressed if they made a mess cooking so this didn’t happen as much as it could have done, and the two metres of pink gingham I bought twenty years ago will never be transformed into a cute pinafore dress for my elder daughter, Emma. The poet, Emily Dickinson observed, ‘That it will never come again is what makes life sweet.’

Another jolt is the realisation that there are definitely places that I will never visit again—people I won’t see again—books I’ll never read again, and films that I’ve seen for the last time. Even much-loved ones. When I was young I felt that life would go on forever. But having a husband with a life-threatening illness forced me to accept that life runs out. This is one of the many reasons that my treats list has been so important to me in recent years. If there are things I long to do then I want to get on with them. Now. Somebody once told me that being grown up is when you stop taking things for granted. Maybe I’m more grown up than I thought I was.

I took all these things into account when I finally replied to Molly’s question: do I feel like I’ve lived a long time. I said that I think I’m getting close to feeling that. And I was able to give her a practical demonstration of my grownupness recently after she was given a very smart record player. She, like so many young people, appreciates the charm of vinyl and is building up a record collection, not dissimilar to the one I had at her age. For a while she appeared to enjoy using her new turntable. All seemed to be going well but eventually she emerged from her room, looking very downcast. ‘Everything sounds so fast,’ she said, unhappily. From the benefit of my relatively long life I enlightened her about the all-important difference between 45rpm and 33rpm.

My final word is on someone who is only in her mid-twenties but has already packed a huge amount into her life. Recently I did the second in my chain interview series.  You can read more here.