The number of women having sex under the age of 16 is rising, an NHS survey suggests.
Over a quarter of women aged 16 to 24 said they first had sex under the age of consent (16) – a higher figure when compared to previous generations.
The Health Survey for England 2010 found the trend to be "less clear" in men.
Just over two in ten (22%) men aged 16 to 24 reported having sex when they were younger than 16 – a figure similar to that of those men aged 25 to 69.
The survey found the average man and woman typically become sexually active at 17.
Of those sexually active respondents aged 16 to 69, 12% of men reported contracting a doctor-diagnosed STI compared to 9% of women.
Furthermore, the same proportion of men and women (2%) said the have had more than one STI in their life so far.
"This year's report paints a picture of sexual behaviour which is changing over the generations with younger women tending to begin having sex younger," said Tim Straughan, Chief Executive of the NHS Information Centre.
"These findings will be of interest to the NHS in tackling matters such as sexually transmitted diseases and contraceptive services."
The survey found 17 is the average age at which both men and women become sexually active.
Men typically have an average of 9.3 female sexual partners in their life so far, while women reported a mean of 4.7 sexual partners.
However, a "substantial proportion" of young people aged 16 to 24 said they have never had sex – 26% of women and 32% of men.