(hollyscoop.com) - Jennifer Aniston 's reps have already denied that she's pregnant, but Star magazine is still running with their story. A few weeks back the magazine claimed that Jenn was pregnant with John Mayer's kid, and now they're claiming she's having twins! Apparently Jenn has been undergoing fertility treatments in a bid to get pregnant before her 40th birthday. "She knows her baby-making years are limited," says a source. "It's hard for her to think of anything else - she has babies on the brain!" It gets better! Apparently John, who is an infamous womanizer, is really excited about the thought of being a dad and has started buying up pregnancy and parenting books. We want to know who this "source" is. Do they live with John or Jenn? It sounds a little absurd to us, but than again Star magazine has surprised us in the past. What are your thoughts?