The concept of has piqued such a lot of interest last week that I've been giving some more thought on how to legitimise this vanity quest in the observant eyes of others.
I mean, it's no use giving your little sister's birth date for gym membership, if you look all and more of your 40-plus (-plus) years and her year of birth makes you a supposed 32.
The gym jocks and bunnies will be raising a sceptical eyebrow (if they haven't made their Botox appointment this summer).
The biggest ager of all is baldness. If you are 18 and the size of your forehead is increasing, the great unwashed will put you down as 32. The age of your big sister/half sister.
The second biggest ager is, arguably, the degree of greyness of the hair you have left, whatever your age.
Unfairly, this is quadruply so if you are a woman. Particularly the baldness.
Silver foxes or grey nomads
If you are a man — again unfairly — the greyness can work in your favour, however. Think George Clooney, soccer coach Jose Mourinho, or even Barack Obama.
Grey can be hot and a bad dye job that's way past it's sell-by date — think Paul McCartney, Sylvester Stallone, Charlie Sheen — looks bad and screams "I really am quite old, you know".
Some other famous names — Tom Jones, Clive Palmer, Rupert Murdoch — have seen the light (and shade) of late and have dumped the dye for a more age-appropriate, natural look. And they look all the better for it.
Hairdresser Jack Morton is Australia's Creative Colourist of the Year 2014 but even he counsels not disguising the grey too much, whatever your age. And whatever age you are trying to pull off.
"It depends what type of look you want but men can look distinguished with grey hair," says Morton.
A colourful opinion
Nevertheless Morton has a very large male clientele, a good percentage of them executives wanting to dye their grey hair. Some come in every fortnight for touch-ups.
It is not as drastic as it sounds. Morton says that — in the right hands — men's colour is subtle. The trick is to get in relatively early. If more than 20 to 30 per cent of your hair is grey, it look obvious if you start dyeing it.
"When you start going grey you can get good results blending the grey hair. It's still salt and peppery," Morton says.
"The products used on men cover 70 per cent, whereas women want total coverage (of grey hair)."
There are professional products specifically designed for men's hair.
"Or it's down to the application," says Morton. "A high percentage of grey is around the hairline so there is some craftmanship involved."
So, do not try this at home.
It's not as high-maintenance as it sounds. You can be in and out in 40 minutes, and the dye's designed to slowly fade out. (Or of course it's cut out if you like to keep yourself looking sharp with cuts every three or four weeks).
Some salons have payment plans for men because, with their more regular hair cuts, they have a higher frequency of colour jobs to women.
"Men come in more often," says Morton.
Are you one of the many men who have joined the "dark side"? When did you start covering your greys? And has anyone ever commented?