On my 58th birthday, I've started to question what it means to be happy – and what it means to be angry

I am 58 years old, which means I am writing this in a size 20 font and I got a Lakeland cling film dispenser for my birthday. Oddly enough, both things are related.

Six months ago I developed dry eye disease, which means I can’t lubricate my own eyeballs and have to use artificial tear drops every couple of hours. It also means that my eyes get tired quicker, hence the massive font. As for the cling film, every night, I put myself to bed with squares of the stuff over my eyes to create “moisture chambers”, which prevent my eyes turning to pumice stone while I’m asleep.

Apparently it’s quite common in women “of my age”.

It’s weird when something goes wrong with you; some people cope better than others. I spent two months in a state of paralysed shock, convinced my life was over; now I just get on with it. Yes, it’s annoying and upsetting, but at my age it’s an occupational hazard.

Being in your late fifties is a funny time. You’re on the cusp of people offering you their seat on public transport – sometimes I can see young people on the tube eyeing me up, in the same way I sometimes eye up young women when I’m not sure whether or not they’re pregnant. I can see them thinking, “Yeah, she’s knocking on a bit but she’s not that old”.

And I’m not, I’m not “old-old” – but then my mother, who is 88, doesn’t think she is “old-old” either. Properly old people, it would seem, are always a few years older than you are.

What I am is firmly “middle-aged”, which is something that I find both glorious and a teeny bit horrific. On the plus side, I am very secure in my own skin. I can’t remember the last time that I felt properly, deeply embarrassed and I know how vital it is to have a hobby.

When you are young, all you really want to do is get off with boys – hobbies are for losers. Now I know that there are hordes of women out there all busily knitting, crafting, sewing and painting, quietly keeping themselves sane by keeping their hands busy – otherwise, who knows, we might rise up and start killing in our droves.

Anger has been a huge part of my life since turning 50. Obviously you have to manage your anger, because it’s very important that it never runs out. Fury can be a positive driving force: I feel very much that I have to keep waving a flag for older women in comedy, for instance. The day I retire will be the day I wake up and don’t feel monumentally pissed off about something. Anyway, I’ve decided I’m actually at my prettiest when I’m furious – I have a sort of rosy pink-cheeked glow about me and I kind of sparkle.

The downside of being 58 is the sudden realisation that one has no idea what the future holds. I don’t know how many holidays I have left; I don’t know how much money I’m still going to have to earn to “see me right”. It’s a bit like being in your early twenties again and wondering how the hell this is all going to make any sense in the end.

I’m also very aware of how other women are dealing with ageing. I’m suddenly really jealous of women who are fitter than me and have sussed out their diet and exercise regimes. My sister is 60 and a size eight, but these days I’m fatter than my mum. I keep bumping into old mates who have given up sugar and/or booze and are back in jeans they bought in 1993, and I’m furious at myself for letting the yoga go because I used to be amazing. I’m livid that all my trousers need to be elasticated and yet I can’t quite bring myself to go to the gym. I sabotage myself on a daily basis.

The race is dividing – the ones in lycra are pulling ahead, and I’m with the chubby puffers at the back. We never really leave the school playing field, do we?

Nevertheless, recently I have started watching women of my age more closely and I’m not just checking out their body mass index (whatever that is) – I’m looking to see who looks contented.

At the moment I’m rehearsing a show in Clapham, a delightful and leafy place presently in the grip of a vegan epidemic, which is fine, because there is also a brilliant butchers, and what I’ve noticed is that the women walking dogs look the happiest. It doesn’t seem to matter what kind of dog it is, although there is a woman who walks a black Scottie who is positively radiant, and this, I’m beginning to suspect, is the key.

I need a dog; I need something to drag me off the sofa and round the block. Just a little one who doesn’t like big walks and only does small poos. Dear reader, my dachshund cravings are almost out of control. I shall keep you posted.