But they should not despair, as the best sex apparently happens in the fifties, while sexual confidence peaks between the ages of 60 and 69.
The Sex Census 2012, which involved almost 25,000 respondents, suggests that 25 percent of those aged 30 to 39 are unhappy with their sex lives owing to money worries and the demands of modern life.
In the same age group 35 percent said caring for babies and young children was having a negative impact on their sexual relationships as they were just too tired.
But as the respondents got older their satisfaction levels increased. Of those between 50 and 59, 52 per cent said they had a good sex life, with only a fifth saying they were unhappy.
Moreover, at age 18 women rated their sexual confidence at only four out of ten, while those aged 60 to 69 rated theirs at six out of ten.
The survey was funded by the charity Relate and the Ann Summers shop chain.
“We know from previous research that the thirties can be a difficult period for some,” the Daily Mail quoted Paula Hall, sex therapist for Relate, as saying.
“Pressures such as mortgages, children and work can really hit hard in this decade, but combined with the impact of a double dip recession, it creates a pressure cooker for our relationships and sex lives and naturally something has to give.
“This age group is always a tricky one. The pressures to have it all are well documented but it’s important that people don’t give up on their sex lives.
“The results tell us that this age group actually want more sex, so people need to take time to work out what’s stopping them.
“It could be a communication barrier, or it might be the fact that you aren’t putting time aside for each other – whatever it is, having an open discussion can help get your sex life back on track,” she added.