Women in their 20s earn more on average than men of the same age, according to newly compiled figures.
Between the ages of 22 and 29 a woman will typically make £1,111 more than her male counterparts, suggesting a reversal of the gender pay gap.
But the story is vastly different for workers in their 30s - a comparative analysis of earnings between 2006 and 2013 showed.
By 2013, a man who turned 30 in 2006 would on average have been earning £8,775 more than a woman of the same age, it found.
O2 HR director Ann Pickering said: "While women are earning slightly more than men in their 20s, they are still overtaken by men later in life - and the reason is simple. Women are playing catch-up when it comes to reaching senior well-paid positions.
"If women are not in the same roles as men, how can they be on the same wage?"
Sam Smethers, chief executive of the Fawcett Society, which campaigns for gender equality, suggested more senior roles would go to women if they were offered on a 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."
Research published earlier this week found that women were working the equivalent of one hour and 40 minutes for free thanks to a pay gap that sees them earn an average of £8,542 less a year than men.
The survey by the Chartered Management Institute and XpertHR found that, across all ages, women earned an average of £30,612, compared with the £39,136 paid to men in equivalent roles.
Additional reporting by PA
