They may not be engaged yet, but Sean Penn and Charlize Theron are already planning the details of their future wedding, including how many guests they hope to invite!

An insider close to the couple tells Life & Style magazine that the pair met at Malibu restaurant Tra di Noi to discuss specifics for their big day.

“They are going to use a wedding planner,” the insider reveals, “but they brought along Charlize’s mom, Gerda, and Sean’s mother, Eileen, to discuss strategy.”

Sean Penn & Charlize Theron Get Affectionate at Met Gala!

And according to a second insider, a few elements have already been finalized!

“They plan to have 200 guests on the beach in Malibu sometime in August,” the source tells the mag. “Sean wants his musician brother Michael to be his best man, and Charlize has respectfully asked her mom to be her maid of honor.”

It's a big step for the couple of five months, but based on their recent behavior, a proposal appears to be just around the corner! At Monday's (May 5) Met Ball, the two couldn't keep their hands off each other, flirting the whole way down the event's lengthy red carpet.

So is Charlize's 2-year-old son Jackson going to play ring bearer? Only time will tell!