How did Jun know this??

Jun to Po: "Why should you be in a rush? Seeing him today, I guess, at most, you'll just end up staring at each other. I'm telling you, during the first six months of dating him, even holding hands is an achievement. And it will take two whole years before you two get to kiss. As for "going to his room"...I'd say it will take up to five years"

Is Jun just guessing this based on Thame's reserved personality or is he speaking from personal experience? 👀 Like this was way too specific, am I crazy or he is alluding to the fact that JunThame maybe had a thing in the past?