Credit: Ryan Caliendo/; Mari Sarai/WireImage

From precocious cutie to pumped-up hunk!

Jonathan Lipnicki became a star at age six when he played Renee Zellweger's know-it-all, bespectacled son in Tom Cruise's smash 1996 film Jerry Maguire.

A decade-and-a-half later, Lipnicki's all grown up -- and super-duper buff!

Now 21, Lipnicki showed off his incredibly chiseled, buff body in a series of shirtless, sexy new photos.

Lipnicki -- famous for uttering the line "Do you know the human head weighs eight pounds?" -- has a Star of David on the left of his torso. In other pics, he flexes his impressive pecs and abs during resistance training, weight lifting and pull-ups.

As it turns out, the former child star of Stuart Little, The Little Vampire and other flicks is still working as an actor, with the films Tag and For the Love of Money already wrapped and in post-production.

Another one of his fitness secrets? He competes in Brazilian Jiu Jitsu. "I'm a blue belt, almost purple," he recently tweeted.