Women over the age of 40 are now having more babies than those under 20 in Britain for the first time since the 1947 post-war baby boom.
A report from the Office for National Statistics (ONS) for England and Wales found there were 15.2 live births per 1000 women aged 40 and over in 2015, compared to 14.5 for those aged under 20.
The figures show the fertility rate among older women has more than trebled since 1982.
They also reflect the long-term decline in the teenage pregnancy rate, which has almost halved from its level of 33 births per 1000 teenagers in 1990.
The average age to have a child is now 30, a figure that has been increasing since 1975. The ONS report also revealed that more than a quarter of births in 2015 were to mothers born outside the UK, the highest level on record.
The percentage has increased every year since 1990, when it was 11.6 per cent.
The long-term rise in babies being born outside marriage or civil partnership has also continued, the ONS said, with 47.7 per cent of all babies in 2015 born outside marriage or a civil partnership, up slightly on the previous year.
The report said: "In most developed countries, women have been increasingly delaying childbearing to later in life, which has resulted in rising fertility rates among older women.
"This may be due to a number of factors such as participation in higher education and the labour force, the increasing importance of a career, the rising costs of childbearing, labour market uncertainty and housing factors."
A spokeswoman for the British Pregnancy Advisory Service, said the trend towards older motherhood was "here to stay".
"Rather than bemoaning this development, we should seek to understand and support the decisions women make," she said.