Women are as young as the boyfriend they feel, say researchers, who believe having a younger man makes women feel four years younger than they really are on average, The Sun reported Tuesday.

By comparison those who pair off with men the same age or older don't enjoy as many outdoor activities and don't mix with a younger crowd.

Those who do — like Hollywood couple Ashton Kutcher, 32, and Demi Moore, 47 — feel happier and younger, according to ToyBoy.com, which conducted the research.

"Whether it means going out more, dressing differently or trying new things they wouldn't normally have done, it does seem having a younger man is the answer,” said a spokesman for the dating website.

"The 'Cougar' dating trend is another great symbol of empowerment for women and it's spreading throughout the world," he said.

Researchers asked 1,000 women aged between 18 and 65 how young their man made them feel.

The average was four years but one in ten said their partner had made them feel ten years younger — and the greater the age gap the happier a woman is likely to be.

Older men were lambasted for being too grumpy by 27 percent of women, 36 percent said they were set in their ways and 20 percent said they were boring.

But three in ten older women don't completely trust their partners not to run off with someone their own age.

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