I can tell when my life’s going OK. My stray thoughts are not about what a loser I am but about what a terrible footballer I am. Why didn’t I shoot when I had that chance? Why did I pass to the opposition? And, oh dear, I wonder how Diego’s knee is?

For almost a decade I’ve been playing football on Saturday mornings in a local park in London. For the first few years I was a fair-weather visitor, shy about it. I’m not much of a joiner and I don’t have much chat about the transfer window, so I felt awkward and almost stopped going. A couple of others were middle-aged and rusty like me, so they probably didn’t really want another old guy getting in the way. But I gradually felt that they didn’t mind me being there, that I was a valid part of the mix.

It’s a couple of steps up from jumpers for goalposts. It’s plastic self-assembly goalposts for goalposts and fluorescent bibs for one of the teams. One of the old guys, Keith, brings the kit. Recently he asked everyone for a fiver for some new stuff. That’s all I’ve ever paid in ten years.

There’s a pool of about 40 men (in the early days a brave young woman sometimes played). You sign up by WhatsApp during the week and there’s room for about 26 people. If there are more than 20, we make three teams, which is nice in the summer as it gives one a breather. Only once or twice have the requisite 16 failed to enroll and only once do I remember it being full when I wanted to play.

About half are student age, a few barely out of school. Some are seriously good. A few can dribble right through a defence or tee up a shot with a deft juggle-touch. There’s a pair of brothers from Kosovo who seem to me to be worth the attention of a Premier League scout. And there are a handful more whose skills are sometimes jaw-dropping. Part of the pleasure of playing is just watching others, even if it does mean being nutmegged for the third time that day.

London’s diversity is fully reflected. Most people are black or brown. There’s a Mo, an Ibrahim, a Nitesh and a few with African origins and ancient names: Ishmael, Abraham and Joel. ‘This is like being in the Bible,’ said Greg once.

Greg is the group’s proud founder. He’s a geezer, is Greg. Don’t tell the missus what a bender he was on last night, that sort of thing. He’s an estate agent but keen to defy the stereotype: don’t tell head office etc. He enjoys being the father figure to the youngsters, tearing them off a strip if they’re late – but in a semi-ironic way, aware there’s nothing much at stake.

Or maybe there is. Once there was a near-fight. A row over a foul led to some nasty insults being thrown about, as well as offers to take it outside, as it were. The two men stormed off in separate directions, and it was suggested that the one deemed chiefly responsible for the ugly scene be banned. But Greg said no, he’s bloody well going to come back and shake the other guy’s hand and learn to be less of a prick. I admired him for that.

There’s one rather tough guy of whom I’m a little nervous. He seems to barge me a bit when there’s a corner and looks like he wants to call me a posh idiot. I think he’d like to meet me in a different context: for example, in a pub. I always hope I don’t accidentally foul him.

Talking of which, there’s a tricky grey area in games like this. Sliding tackles are frowned upon: yes, they’re part of the game when it’s played seriously, but at this level the risk of injury isn’t worth it. Therefore, although I clearly won the ball, it was wrong of me to slide in on Diego last week. I felt bad as he hobbled off home. I still feel bad.

Do we start by picking teams? Isn’t that a form of schoolboy humiliation? Thankfully the selection process is politely veiled. A couple of captains are chosen, they have a private conference and a minute later someone chucks me a bib or doesn’t. Thank God.

I’m not the sort of writer who offers a moving final paragraph on the mental health benefits of understated male-bonding camaraderie. These things are hard to gauge. Did football help me through my depressed phase a couple of years ago? I turned up less regularly and was even less chatty than usual. For a couple of hours, it took my mind off my mind. But maybe it also gave me a sense that it was all right to be quiet and distant; I was still accepted and my teammates still said ‘Well played’.

My advice to middle-aged dabblers in football is this. Don’t be shy. Those lads in the park might be nippier than you ever were, but don’t assume that they don’t want you to join them. Get stuck in and know again that wonderful boyhood feeling of washing caked mud from tired legs.