Women earn more than men until they hit their 30s when they fall behind, but the change is almost entirely explainable through parenthood and personal choices rather than sexism, according to experts.

Using data from the U.K.’s office of National Statistics, the Press Association found from 2006 to 2013 women aged between 22 and 29 earned roughly $1,700 more than their male counterparts. However, the wage differential between men and women flips in a big way when people move into their 30s.

A man who turned 30 in 2006 would rake in, on average, $13,464 more than a women by 2013. Campaigners and activists pounced on the figures claiming the working world was still stacked against women, and that for senior positions in private business, it’s still a mans world, entrenching the gender pay gap.

Ann Pickering, Human Resources director at telecomms giant O2, claimed the reason for the gap was that ”women are playing catch-up when it comes to reaching senior well-paid positions.”

Sam Smethers, chief executive of the the womens lobbying group The Fawcett Society, said there would be more women in top jobs if they were offered on part-time or job-share basis. ”Unless there is good reason not to do so, that should be a company’s default thinking,” she said.

“Sadly the opposite is true: once you get to certain level it’s a full-time role, which excludes many women from roles they would be perfectly capable of doing,” she added. But according to economists at the Adam Smith Institute, the report’s figures on their own can give a misleading impression on gender wage gap.

Kate Andrews, research fellow at the Adam Smith Institute, told TheDCNF:

Even numbers rarely speak cold, hard truth – – especially when it comes to the gender wage gap debate. The Press Association calculates that by the time women reach their 30s, they are earning thousands of pounds less a year than men; their data, however, comes from the Office of National Statistics, which found that in 2014 (latest figures), women’s median salary was slightly higher than men’s up until the age of 40. How is this possible? The ONS calculates hourly wages rather than yearly salaries to control for number of hours worked.

According to Andrews, the PA numbers ”calculate yearly, take-home income, which is more likely to prove that men work more hours than it is to prove the workplace is inheritly sexist.”

Writing in Forbes, senior ASI fellow Tim Worstall delivered another blow to the argument to sexism explanation of the gender wage gap. ”The correlation is with average age at the birth of the first child: around 30 now for UK women. And that’s the cause of the overall pay gap. Mothers tend to get paid less than non-mothers,” writes Worstall.

Worstall argues that a woman in the U.K. who has two children in her 30s and takes all available maternity leave will have spend two years out of the workforce, putting her at earning potential at risk. For good measure he adds that non-married women married without children earn more than their male peers who who don’t have have children during that decade of their 30s.

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