Julia Clark, a pollster with global market research company Ipsos, says, it’s fair “to consider that some of the ‘under 35’ and ‘over 35’ differences you find are due to the fact that that’s where we draw the line.”

However Clark adds it’s a standard practice among the market research community to use age categories that cut across decades, rather than coincide with them, to accurately group people by life stage. A 20-year-old and a 29-year-old are often at very different life stages, so the first common demographic grouping runs from 18 to 24 (then 25-34). Macro groupings use 18-34 and 35-54, making 35 one of the most common dividers between those who are young and developing a career and those who are older and more established.

Women who want to have children still face anxiety over their fertility post-35 although recent research suggests fertility doesn’t drop as sharply as once imagined. In the US, an increasing number of women are now postponing their first pregnancy well into their 30s to continue education and forge careers. The latest statistics from the US Centers for Disease Control and Prevention suggest that, for the first time in recorded history, women in their early 30s are now having more children than those in their 20s.

There are also financial reasons for delaying children – a 2011 study published in the Journal of Population Economics found that every year a woman postpones having children leads to a 9% increase in career earnings.

Deferred decisions

Dilip Jeste, director of the Center for Healthy Aging at University of California San Diego, says there’s a common misconception that our 20s and 30s will be the best years of our lives, and that things only go downhill later on. In reality, these formative years are riddled with the stress and anxiety of making major life decisions.

A longer life-span in the developed world, coupled with the overabundance of choices in a globalised economy, only makes this process of settling into a career, family and geographic location longer and harder than it was a generation ago.