Ever since I read John Updike’s Rabbit tetralogy, I have felt that the ultimate test of a writer is to capture a single life from beginning to end in the pages of a novel.

The idea of a single life captured through different points in time was behind the TV documentary series 63 Up (I am also 63). Partly for research into my next novel and partly out of curiosity, I find myself asking, who was I at 7, at 14, at 21, and so on? Does looking back on an entire life help us shape who we want to be from now on? Am I still the same person – or someone entirely different? After all, every life has two distinct aspects: the external and the internal.

I want to examine the span of my life, like the 63 Up subjects, to see where I am and perhaps where I want to be, as my life approaches its own closing chapters. I want to try to shrink it down to something like a few sequential thoughts, if only to find out if there is any point in the exercise. So here goes…

As a child in working-class west London, I was, my mother proclaimed, “a dreamer” living in, according to school reports, a “little world of his own”. But I was also, like all hyper-introverts, vulnerable to bullying – both at school and, to a greater extent, by my elder brother. By my teenage years, I had become uneasy and restless. I indulged in booze, soft drugs and pointless acts of vandalism. This followed a decision I made to abandon the shy, bookish boy I was, lest I be bullied any more. In short, I re-invented myself, as I have had to do repeatedly.

At that time I had already determined to achieve several things in my life – primarily that I would escape my dull, suburban, penurious background, by becoming a journalist. I was determined to avoid the 9-5 at all costs. I also wanted to generate thoughts that were worth having, rather than the chaotic ego-driven chaos of my consciousness.

I was also desperate to escape the zeitgeist I was born into, the sterile “nothing but” philosophy of British pragmatism and scientism (as in, say, love is “nothing but a series of electrochemical reactions”). I wanted to find a richer philosophy of life. I determined to live a life of extremes, to somehow generate a story worth telling. Finally, I was set on the idea I would never marry or have children. Instead I wanted, as teenage boys do, to have brief, passionate affairs with as many women as possible.

It started well. At the age of 19 I had been plucked from my trainee status at a local paper to work on the then-powerful music press. I travelled the world, interviewing the likes of David Bowie, Freddie Mercury and Fleetwood Mac.

On the outside my life was going well and was a lot of fun, but much was hidden – including my anxiety. My urgent ambition acted as a way of escape, not only from my background but from my own mind. By 28 I had founded a magazine, and made enough money to attend the LSE. I had friends, a good family and plenty of cash. However, my mental health was fragile. After the break-up of an important relationship and, completing my degree, I was offered the editorship of a major London magazine, a task I was ill-suited for. After three weeks, I resigned, suffered a breakdown and became suicidally depressed. It turned out social mobility wasn’t as problem-free as advertised.

I recovered by the age of 31, but I felt effectively unemployable. That same year, my mother committed suicide. It was a devastating low point that would be beyond the stretch of a work of fiction. Yet within a year, I answered an ad in a newspaper for a job with a TV production company and was offered it. I married, at the age of 35, a college lecturer from a background similar to mine – also struggling with mental-health issues. My wife gave birth to two daughters; with this, for the first time, I felt something approaching stability.

It was now that I began at last to put together one of my childhood goals – a philosophy of life, since the results of my external ambitions had been so unsatisfactory. Prompted by investigations into my own depression, I started to study Zen Buddhism, after reading Alan Watts, the British philosopher who popularised eastern philosophy in the west. I believed I was finding what Taoists call “The Way”. The breakdown had forced me to put a mirror up to myself, something in my furious ambition I had been desperate to avoid, sensing only chaos within.

I was sacked from the TV company and I finally sat down to write a novel. As the rejection slips piled up, once more I was feeling like a failure and wondering what the hell I was going to do in the future. But at least I had become close friends with the elder brother who had (in my mind) so persecuted me as a child.

At 43 I found a publisher for a book telling the story of my breakdown and my mother’s suicide. It became a critical hit. Then, in 1999, I finished my novel White City Blue. Its protagonist, Frankie Blue, reappears in my new novel, When We Were Rich, as he will, Rabbit Angstrom fashion, in future volumes. White City Blue won the Whitbread first novel award, I was in a new relationship, my partner had given birth to another daughter, my third (so much for not wanting marriage or children). My career was peaking. People stopped me in the street from time to time and asked me for my autograph.

By my mid-50s the bubble had started to deflate. My few media appearances had been more or less disastrous, with my ADHD producing more and more eccentric performances – weird outbursts and losses of temper. My books, although well-received, fell very much short of being best sellers. I was dropped by my publisher and only by the skin of my teeth made it to another publisher. My face was beginning once again to show the gravitational sag of the lifelong melancholic.

Come, finally now, 63 and, on TV, 63 Up. My depression and ADHD are under control thanks to medication, but they have continued to occasionally flare up – the most recent episode of depression lasting a whole year in 2015. I am divorced a second time, but my four daughters are an inexhaustible source of meaning. As for the passion – well, unlike John Betjeman, I have no complaints.

So how can I sum it all up? It’s been an eventful drama, as I hoped it would be. And now even more peculiarly, for someone who was the son of a greengrocer, I find myself in a fairly long-standing relationship with a woman whose grandmother was a countess (and whose grandfather the governor of the bank of England). Social mobility has more or less seized up in this country, and I’m beginning to understand why. It’s not just about opportunity – as Professor Green remarked when he was briefly married to Made in Chelsea star Millie Mackintosh – it’s like visiting a foreign country: very disorienting.

It’s a journey that has taught me an immense amount. I did end up – I hope – “having thoughts worth having” and even a philosophy of life. As for the “give me the child at seven and I will give you the man” maxim tested by the 7 Up documentary series, I am an entirely different person to that introverted seven-year-old – and also exactly the same person. Who do I want to be now, all these years on? For the most part my ambitions have narrowed to someone who is, simply, alive, healthy and at peace.

Like the 63 Up crowd, I’m not sure I’d change a thing. There has been misery, but my story includes many moments of shining happiness. Then again, I’m not sure that I wouldn’t change a thing either. It turns out that the main lesson I’ve learned is that “not being sure” is the essential condition of life. With that in mind I’m looking forward to what happens next. Only, I’m not.

Because looking forward is pointless. So is looking back – because every time you do so, the picture changes. The past is no more fixed than the future. What I think about my life is my life. Until, of course, I think about it next time.

When We Were Rich by Tim Lott, is published by Scribner at £16.99. To order a copy for £11.99, go to theguardianbookshop.com