The 49-year-old actor has filmed a video blog in which he confesses he has a huge crush on `The Amazing Spider Man` actress - who is 27 years younger than him.
In the comic video posted on his official website, he says: "Emma, I think you`re all the way beautiful. Not just pretty, but smart and kind-hearted. And if I were a lot younger, I would marry you. We would have chubby little freckle-faced kids.
"We`d laugh all day long, go camping and play Yahtzee. Tell ghost stories by the fire."
Jim - who split from former Playboy model Jenny McCarthy after five years together in April 2010 - acknowledged the age gap in the video, and jokingly admitted a relationship between the pair would be inappropriate.
He added: "And every day, for the rest of your life, you would thank God that I was the appropriate age for you. But I`m not. I`m 49.
"I have lines on my face, sometimes a little gray in my beard, and it takes me a little bit longer to pee than it used to."
He signs off the video by wishing Emma - who is rumoured to be dating her `Spider Man` co-star Andrew Garfield - the best with her career.
She said: "Anyway, I just wanted to let you know how I felt. I think you`re very special and I wish you continued success and artistic fulfilment. But most of all, I wish you love and contentment."