I found myself contemplating Julie Bishop’s bosom the other night. She was waxing lyrical about external exams: all well and good, as you’d expect from the Education Minister. But what struck me about the Bishop bosom is that we barely see any of it. Hardly a hint of cleavage peeps out from those perfectly tailored suits.

But then, nor do we ever get to spy a Julia Gillard cleavage either. Not even a suggestion of one. Come to think of it, Federal Parliament is devoid of cleavage. Which is perhaps quite a trussed-up tailoring feat, when you consider that there are 64 pairs of bosoms across both the House of Reps and the Senate.

Perhaps in Australia we’re just a little shy of mixing power and professionalism, with the fact of our femaleness. Unlike our more raunchy sisters in Britain.

There, in the House of Commons, home secretary Jacqui Smith has been applauded for her display of ample cleavage on the floor of parliament. Even the poison pen of The Washington Post’s fashion editor, Robin Givhan, couldn’t help but dip into some pretty colourful ink when she described 45-year-old Smith’s exposed decollete as ”a full- fledged come-on”.

But by no means was that meant to be derogatory. Givhan – who has won a Pulitzer Prize for her fashion commentary – insists Smith’s ample womanliness was ”presented so forthrightly”, that it was ”all part of a bold, confident style package” to be commended. While Givhan is of the view that showing a bit of cleavage is a way of requesting ”to be engaged in a particular way”, she nevertheless insists that ”it doesn’t necessarily mean that a woman is asking to be objectified, but it does suggest a certain confidence and physical ease”.

However, it seems such female displays of ”confidence” and ”ease” are fine – up to a point. An age point. There is, apparently, an unwritten rule about when it’s no longer appropriate for a female to flaunt it. I’ve no idea who wrote the rules, but supposedly women intuit the correct age at which one should cover up, button up, and ditch the heels for comfy flatties.

If you are wondering where the cut-off age might be, think Hillary Clinton, and count backwards some 15 years. A furious storm of media commentary has erupted over a tiny peek of, you guessed it, Clinton’s cleavage. Two weeks ago, while debating the cost of education in the Senate, Clinton’s black v-neck top, seen under her rose pink jacket, just happened to reveal a hint of cleavage. ”Not an unseemly amount,” according to The Washington Post, ”but it was there”.

The newspaper’s fashion mistress, Givhan, declared it ”an exceptional kind of flourish”. Indeed she was so affronted by such a womanly display from Senator Clinton that she likened it to eyeing Rudi Giuliani ”with his shirt unbuttoned just a smidge too far”. Warming to her theme, she went on to suggest ”it was more like catching a man with his fly unzipped. Just look away!”.

The problem isn’t the cleavage, or the bosom. As we know from Givhan’s thrilled critique of the British home secretary’s forthright display of her buxom virtues, the fashionista hasn’t anything against a womanly flourish. It’s just that the woman should not be of a certain age. In other words, she shouldn’t be as old as Hillary Clinton.

Clinton will be 60 this year. Such maturity, it would seem, calls for female modesty. According to Givhan, Clinton should drop the girl stuff and stick with her ”desexualized uniform” of a black pantsuit.

So with age must a woman un-sex herself? Is that why I’m hearing echoes of Lady Macbeth’s ”Unsex me here” lurking in these silly shadows? When a mature woman has got some serious work to do – or in the Lady’s case, some brutal, murderous, treachery in mind – must she strip away, or indeed cover up, any sign of her femaleness?

Are we still so dreadfully afraid of the power of a woman’s sex, that when she is past her mid-40s , and no longer of fertile age, we’re affronted, even embarrassed by a reminder of her sexuality? It would seem the answer is yes, if the current ”cleavage conversation” in the US is anything to go by.

Even Australia’s former Sex Discrimination Commissioner Pru Goward felt the need to point out a sort of ”un-sexing” of herself, when she entered the NSW Parliament. ”Now I’m 54, I’m not cute anymore,” she told an audience of women when complaining of the rampant sexism in politics. While I suspect Goward meant to imply that she was no longer naive, there was nevertheless a hint of lament in her statement.

But there was no such gentle lament from the late feminist icon Betty Friedan. Her panic was palpable as she wrote about the ”devastating terror of not being young”. But most infuriating for Friedan was the inherent sexism in ageism. While ageing men – think Rupert Murdoch – become older, wiser, wealthier and more attractive to young women; ageing women, on the other hand, are noted more for their tendency to shrivel – physically and sexually.

The tragedy is that while cleavage displays are mostly left to the very young, older and wiser women at their most powerful peak are still stuck with the need to wear a buttoned up suit to be taken seriously. While playing that game, both genders lose.