Over the last 10 months, I have been feeling low - literally.

I have been avoiding high heels because wearing them causes my back and right hip to hurt.

Flat and low-heeled shoes have been my reluctant footwear of choice and I feel short, squat and pretty miserable in them.

I miss the three-inch heels I used to wear, which made me tall and confident.

The pain in my hip and back isn't the only ache I have to bear with these days.

I recently realised that not a day passes where I am completely pain-free, which has led me to this conclusion: There's no denying it anymore, I have hit middle age.

The Oxford English Dictionary defines middle age as "the period of life between young adulthood and old age, now usually regarded as between about 45 and 60".

Going by this definition, I actually entered middle age seven years ago.

However, 53 is apparently the new 45.

In 2013, British healthcare provider Benenden surveyed 2,000 people for their views on middle age. The consensus: 53 - not the 40s - is the age life changes.

Higher life expectancy and healthier lifestyles mean the average person now feels it's not until he is into his 50s that he begins the downward curve, said Benenden.

In fact, about half of those surveyed said there isn't really a "middle age" stage of life anymore. Eight in 10 said middle age was more a state of mind than a physical milestone.

No matter how one might protest against the concept of middle age - and the stereotypes that go with it - I doubt anyone would disagree that hitting your 50s is a big deal.

Getting to 50 is a milestone the way 30 or 40 or, for that matter, 60, isn't.

I have witnessed changes in myself since turning 50. Here are eight of them:

1. My poor aching body

These days, there's always something or other wrong with my body. Even if I am not actually sick, there will be a twitch here, a soreness there or a strain that doesn't go away.

It didn't use to be like that.

In the past, aches, pains, coughs and colds disappeared after a few days of rest. They didn't hang around like an unwelcome guest.

Weight, too, was something that just melted away. I could lose 2kg in a week just by running. Now, losing 200g is a struggle even if I diet and exercise. (Middle age is when your age starts showing around your middle, said the late comedian Bob Hope.)

I still remember those days when I could survive on minimal sleep .

When I was in my mid-30s, an editor marvelled at how I could pull an all-nighter at work, go home for a few hours and be back in the office looking "fresh as a daisy", which was how he described me.

The daisy is looking rather droopy now. There are only so many late nights I can take and, if I stay up late, I look and feel it the next day.

In fact, I increasingly get comments like "you look tired" when I'd actually had a good night's sleep.

2. Obsession with health matters

Because my body is slowly but surely breaking down, I've become pre-occupied with my health.

The knowledge that 65 per cent of my life is over - assuming I live to the average life expectancy of 80 - is a sobering one.

The realisation that age brings diseases has made me morbid. I am curious to know what lies ahead. Is that lump cancerous? Is the headache a sign of something more ominous? I need to know.

3. Seeing danger everywhere

While life has become more precious, it also feels more precarious.

My imagination has always been active, but these days, it can get pretty wild. I see danger everywhere.

If I spot streaks of water on the kitchen floor, my first thought is: What if someone slips on it and breaks his hip, gets hospitalised, catches pneumonia and dies?

Horrible thoughts such as these never crossed my mind when I was younger.

4. The long bedtime ritual

In the past, I could get ready for bed quickly - shower, change into something comfy and sleep.

Now, bedtime is a multi-step process.

First, there's the beauty ritual to fight the ravages of time - eye cream, face cream, melasma cream, neck cream, body lotion, nail serum, hair tonic and detailed dental flossing.

Then I have to be properly covered. I have taken to wearing socks to bed. It's unsexy, but it keeps me warm.

I have to make sure there's a glass of water next to my bed should I wake up in the middle of the night feeling thirsty.

Sometimes, I take an antihistamine pill to ward off the morning sniffles or use eye drops to stave off dry eyes.

The room has to be sprayed with a special soothing lavender scent.

Finally, I rub Origins' Peace Of Mind lotion on my neck, temple and wrists to help me relax. I inhale deeply. Only then am I ready for bed - assuming I do manage to sleep, that is.

5. Preoccupation with footwear

For years, I tore around in the highest, thinnest heels I could bear to wear. But because of my hip woes, comfort has become my No. 1 consideration when it comes to footwear.

And, as women know, comfortable shoes are seldom stylish and sexy.

That, for me, has been the saddest aspect of growing older.

6. Fashion posers

When I was young, I wanted to look more mature and achieved that with heavier make-up and formal clothes.

Now, I want to look younger, but how does one keep up with trends without looking frightful, like mutton dressed as lamb?

Can a 50-year-old woman pull off a Forever21 outfit? Off-the- shoulder tops are in fashion, but should I go there? Blue eyeshadow is popular. Dare I risk it?

7. Looking longingly at old photos of myself

The photo on my office security card was taken 12 years ago. I used to hate it because my face looks chubby. Now, I look at it almost enviously because that is such a young and fresh version of me. This bittersweet feeling hits me whenever I look at my old photos.

8. More open-minded

If there is any upside at all to being older, it is that I have become less bloody-minded about things.

I'm more prepared to accept views that are different from mine and I don't feel so rabid about defending myself or getting what I want.

I look back at some of the things I did and said in my 20s and 30s and shudder at how unforgiving I was.

What I miss most about my younger self, though, is the excitement of living life almost dangerously. I miss the adrenalin rush of being impulsive and crazy. I don't have the energy or inclination to be like that anymore.

So the bad news for me is I am well and truly in middle age.

But there is good news.

The French novelist Victor Hugo said: "Forty is the age of youth. Fifty is the youth of old age."

I suppose if I were to live to be 80, I'd look back to the time I was in my 50s and think, how nice it would be to be young again.

Lesson here: Treasure what you have, while it lasts.

• Follow Sumiko Tan on Twitter @STsumikotan