Also in attendance was family friend, Jordyn Woods, who gifted Jaden a large crystal for his birthday.
The family shared birthday cake shots of tequila at the intimate bash in Malibu, California, before Will gave his son some words of advice in a heartwarming speech.
"I'll tell you something my father told me on my 21st birthday. Never break two laws at one time. Because you increase your chances exponentially of getting caught for both. So only break one law at a time," the 50-year-old joked.
Will added: "I'm really proud of you, just the way that you've grown in the past few years is what parents hope for. You take it seriously to contribute to the human family. You just make us proud every single day. So, here's to your 21st birthday today, and here's to you being a full grown man."
Jaden, who recently gave away free vegan meals to people in need to celebrate his birthday, was told by his father that he now had to pay for his own medical insurance.
"Here's to paying your own bills. The accountants are transferring your stuff first thing tomorrow morning," the "Men in Black" star laughed.
Determined to embarrass his son, Will also decided to reveal that it was tequila that was responsible for him and Jada conceiving Jaden.
"I've kept from saying this since you were born. Most of the decisions that developed you were your mothers," he smirked. "I was at work, I wasn't home. Your mother did most of the work, I'm not gonna front."