Children born to older mothers perform better on cognitive tests than those with younger mothers, a study suggests.
The move is a turn-around from 40 years ago when children born to younger mothers performed better, experts say.
Researchers say older mothers now tend to be better educated, more established in their jobs and less likely to smoke during pregnancy.
Experts from the London School of Economics and Political Science (LSE) and the Max Planck Institute for Demographic Research (MPIDR) analysed data from three UK longitudinal studies from 1958, 1970 and 2001 where children's cognitive ability was tested when they were 10 or 11.
The study, published in the International Journal of Epidemiology, found that in the 1958 and 1970 studies, children born to mothers aged 25 to 29 scored higher than children born to mothers aged 35 to 39.
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The role was found to have reversed in the 2001 study.
Lead author Alice Goisis, a researcher at LSE, said: "Our research is the first to look at how the cognitive abilities of children born to older mothers have changed over time and what might be responsible for this shift.
"It's essential to better understand how these children are doing given that, since the 1980s, there has been a significant increase in the average age of women having their first child in industrialised countries.
"Cognitive ability is important in and of itself but also because it is a strong predictor of how children fare in later life - in terms of their educational attainment, their occupation and their health."
