More than a quarter of women now aged 16-24 first had sex when they were underage, compared with just 4% of women aged 55-69, a survey suggests.The Health Survey for England asked 8,420 adults aged 16-69 about a range of issues, including sexual behaviour.For men, the rise in underage sex was smaller - from 15% of 55- to 69-year-olds to 22% of 16- to 24-year-olds.Sexual health experts said young people needed education to ensure they did not have sex before they were ready.The survey was carried out by the NHS Information Centre.It also found that a significant number of the current generation of young people had never had sex - 26% of women and 32% of men.This compared with 1% of 55-69-year olds, and 2% of 25- to 55-year-olds.By contrast, one in 10 16- to 24-year-olds - both men and women - said they had had 10 or more sexual partners.NHS Information Centre chief executive Tim Straughan said: \"The survey paints a picture of sexual behaviour which is changing over the generations, with younger women beginning to have sex younger.\"These findings will be of interest to the NHS in tacking matters such as sexually-transmitted diseases and contraceptive services.\"Rebecca Findlay, a spokeswoman for the sexual health charity FPA (Family Planning Association), said: \"This tends to reflect other research on the issue, but we must remember that most young people under 16 aren\'t sexually active.\"Society has changed dramatically in the last 50 years and the nature of relationships has too.\"Education and information safeguards the sexual health needs of young people and helps them resist having sex before they\'re ready which is why, given this data from the NHS Information Centre, there\'s an overwhelming need for statutory sex and relationships education in schools.\"The survey also found that 68% of men were overweight or obese. Twenty-six per cent were obese, up from 13% in 1993, when the survey was first carried out. Fifty-eight per cent of women were overweight, with 26% of those obese - up from 16% in 1993.