Hugh Hefner, Playboy magazine founder, and Playboy Playmates and girlfriends from left Kendra, Holly and Bridget. - REUTERS

Playboy boss Hugh Hefner has thanked his three live-in girlfriends for keeping him young.

The 80-year-old magazine mogul is famed for having numerous partners living at the world-famous Playboy mansion with him.

At present, Hugh has three live-in ladies, Holly Madison, 26, Bridget Marquardt, 32, and Kendra Wilkinson, 21, and he admits it is their youthfulness which has allowed him to stay young at heart and active in the bedroom.

He told the AFP news agency: "Well, I think that relationships with young people keep you young. I don't know if the sex is better than it was 20 years ago, but the life is a lot better."

Hugh also claims three is the perfect number of women to have in your life and your home.

The magazine boss once had up to seven women living with him at one time, but admits the situation was impossible because of all the bitchiness.

He explained: "I've tried it and all the variation of the theme. That became notorious and also caused conflicts because the girls did not all get along with one another, so I decided to downsize and I wound up with three very special ladies."

Meanwhile, it has been reported that Hugh is leaving US$4 million to his three live-in girlfriends in his will.

The ageing lothario is making sure Holly, Kendra and Bridget will be able to live comfortably when he passes away.

However, he is allegedly leaving considerably more money to Holly than his other lovers.