The "study", as reported in this article and the one referenced to it, is incredibly misleading. The age of 39 does not actually appear to be an age chosen by women in the "study." Take note the study was a sampling, not just women, but of men and women.
Men and women reported that "...the top signs for women that you’re [men are] too old for them to flirt with, and they’re pretty obvious signs of aging: Your hair is going gray, you’ve got a couple of chins, your hair is thinning, and your teeth look bad." Those things are not directly about being 39 or older, as the headline implies, but presenting one's best self. A double chin and bad teeth are not attractive at any age, not suddenly when a man turns 39.
Take note that, as reported, it appears that, men's perceptions of when men lose attractiveness to women, were tabulated right in to the total along with women, thus creating a false perception in the reporting that the conclusions were based on women alone. I state that as I think men make a far bigger deal out of men's hair thinning, than women. I think it's corporate interests above all that drive that insecurity in men, all for financial gain. I'd be curious what percentage of respondents were male vs female suggesting that.
What I did find interesting was,
"Six out of ten women (62 per cent) assume that most men in their late 30s are attached by that age and are not worth approaching." I think this is key for men to be aware of. It suggests opportunities are passing by, if you are always waiting for the woman to approach.
The other was, "No longer being chatted up or eyed up on a night out was the clearest sign for both sexes that a man had become invisible - chosen by 54 per cent of respondents." (again, men and women)
The idea that at 39 men become invisible is just a headline to gain to readership by the articles reporting. Men's SMV does not end at 39 as the headlines mistakenly suggest. In fact for many, it's quite the opposite.