Zach Yadegari is an 18-year-old high school senior from Long Island, NY who founded a calorie-counting app that's worth tens of millions of dollars -- but that wasn't enough to gain admission to Ivy League schools ... and now he's going all LeBron James by taking his talents to South Beach.

The entrepreneur joined us on "TMZ Live" Friday and we asked him how in the world he got rejected from top universities like Stanford, MIT, Harvard, Princeton and Yale.

Zach was still in high school when he rolled out Cal AI, an app that uses artificial intelligence to help people count calories ... all they have to do is snap a photo of their food and the app tells them how many calories are on their plate.

Despite 5 million downloads, a team of 17 employees stretched across 4 continents, and annual revenue projected at $30 million ... Zach tells us why he thinks college admissions officers weren't impressed, and why the admissions process doesn't do any favors for young entrepreneurs.

Zach ended up getting accepted to the University of Miami ... and he tells us why he wants to go to college despite already being a successful businessman.

Catch the full interview on "TMZ Live."