The 24-year-old dancer says that the 42-year-old Latin beauty has the body of a woman half her age, and is not afraid to use it.
"Casper said J-Lo has an amazing body and she's in better shape than any other girl he's ever been with," the Sun quoted a pal a saying.
"He said she's got the body of a 20-year-old. They're inseparable right now.
"It's just about sex - and no one's sure if it has much of a future. But he's having a good time finding out," the friend added.
Dancer Casper started working on the singer's world tour six months ago, but in recent weeks the pair have been getting to know each other on a series of dates.
They have been spotted partying in Las Vegas and leaving hotels after nights together.
A source close to Lopez has confirmed their relationship has developed into "a fun fling", adding: "They're dating and having a good time."