When happy hour is now a nap and my back happily goes out more than I do

You know you're getting old when...

It takes twice as long - to look half as good. And everything hurts: what doesn't hurt - doesn't work.

But enough of the dad jokes.

The thought of ageing has been dawning on me for a while, particularly when I chat with childhood heroes.

(Boasting alert here)

So, last week I had the pleasure of chatting with actor John Waters about his new show, the gothic horror The Woman in Black.

I mentioned that I'd spoken to him many times before, more recently about his one-man show Looking Through a Glass Onion.

His response: "I never dreamed I'd be interviewed for a senior's newspaper. Well, I am 75 so I'm the right age I guess."

Wait. What? 75. It seems hardly any time since he was on Play School for 20 years.

Whoever coined the term "age is just a number" was spot on.

It's no barrier to John's career and nor should it be.

You only have to read the print and online versions of The Senior newspaper to see ordinary people doing extraordinary things.

And the older they get, the more extraordinary and - and daring - their feats become. Just look at how many ultra-athletes are aged over 60. Or 80.

It's really only our bodies that let us down as we get older. Like when you stand up and your knees make that funny cracking sound similar to celery being snapped.

There's that realisation that we're not spring chickens anymore, but more like processed chicken nuggets with crook knees.

Scientists have said that most people feel older or younger than they really are and that has a big effect on their physical and mental health. They call this "subjective age".

They said that your 'subjective age' may be essential for understanding the reasons that some people appear to flourish as they age while others fade.

If your age was based on the way you feel inside, how old would you say you are?

Not everyone ages the same way and it's up to us to keep a younger mindset.

But time for one more dad joke from late actor George Burns. (Come on, indulge me).

"You know you're getting old when you stoop to tie your shoelaces and wonder what else you could do while you're down there."

So, age is not restricted to us mere mortals.

An international team led by Australian research centre ASTRO 3D reports that age is the driving force in changing how stars move within galaxies.

Galaxies start life with their stars rotating in an orderly pattern but in some the motion of stars is more random. Until now, scientists have been uncertain about what causes this - possibly the surrounding environment or the mass of the galaxy itself.

A new study, published in a paper in Monthly Notices of the Royal Astronomical Society has found that the most important factor is neither of these things.

It shows the tendency of the stars to have random motion is driven mostly by the age of the galaxy and things just get messy over time.

"When we did the analysis, we found that age, consistently, whichever way we slice or dice it, is always the most important parameter," says first author Prof Scott Croom, an ASTRO 3D researcher at the University of Sydney.

"If you find a young galaxy it will be rotating, whatever environment it is in, and if you find an old galaxy, it will have more random orbits, whether it's in a dense environment or a void."