Hugh Hefner will turn 91 on April 9

Cooper (left) and Hugh Hefner in 2013
| Credit: Paul Archuleta/FilmMagic

After reports swirled last fall that Hugh Hefner‘s health was declining, the Playboy founder’s youngest son, Cooper, is assuring that his father is in good spirits.”He’s doing fine,” Cooper told E! News about his 90-year-old dad. “My dad has always made the joke that if the mansion was your house, why would you want to leave?”

Cooper, 25, continued: “I think because he has stepped back from the day to day operations of the business, people have thought that his health was not very good. The reality is he has a really bad back — that happens when you’re 90 — and he is enjoying life at the mansion.”

But even at the age of 90, Hefner, who turns 91 on April 9, still lives an active and fun life.“His friends still come over and watch movies,” Cooper said of his father’s activities. “Everyone gets together for dinners. They still do manly night Mondays. And Friday and Saturday and Sunday, everyone gets together.”FROM COINAGE: The Most Expensive TV Shows of All Time

Hefner, who said “I do” to his bride Crystal Hefner, at the Playboy Mansion in Holmby Hills on Dec. 31, 2012, also addressed rumors about his health last September — and set the record straight with his fans and followers.

“I wish the tabloids had informed me a little earlier in the week that I’m sick. I might have cancelled my weekend plans,” Hefner quipped in a tweet.

This past October, former Girls Next Door star Kendra Wilkinson admitted that she worries “every day” that she’ll lose Hefner.

“He’s at that age and I’m not going to lie, every day I open up my social media and I pray that I don’t see what we think might happen,” said Wilkinson, who used to live in the Playboy Mansion.

She added: “He honestly is my family. I don’t even know how to say it. He’s an angel to me in my life. The day that comes will be devastating for me and my family.”