I’m 18 and Built a Multimillion-Dollar Startup. Here’s How I Did It.

This as-told-to essay is based on a conversation with Zach Yadegari, an 18-year-old cofounder and CEO at Cal AI, an AI-powered nutrition and food tracking app, based in Miami. Business Insider has verified the financial claims mentioned in this article. This story has been edited for length and clarity.

I sold my first app at 16 years old for almost $100,000. It was called Totally Science, an unblocked gaming website that allowed students to play games in school. It earned me thousands a year for two years through Google AdSense before I sold it.

Every app or game I’ve built has been to solve a problem in my own life. I was a skinny kid growing up and tried going to the gym to put on weight, but learned very quickly that most results come from diet. My cofounders and I set out to build a calorie-tracking app that integrates AI technology.

I moved to San Francisco a couple of months after launching with one of the other cofounders, and we spent the summer of our junior year in high school there alone, just the two of us, 17-year-olds, building out the team from scratch.

Our app really took off over the next year and a half, bringing us to now, where we are a 30-person team and generating around $30 million in annual revenue.

I’ve been coding since I went to coding camp at 7 years old

My parents put me in a coding camp when I was 7. I didn’t learn that much, but it sparked my interest and showed me what was possible. YouTube taught me the rest. I would spend hours a day watching people program different video games.

I attempted to recreate some of the most complex video games with my own small tweaks. This didn’t quite pan out as a 10-year-old trying to replicate what a team of 100 people had accomplished, but I learned a great deal. After watching “The Social Network,” Mark Zuckerberg became a massive inspiration. He was the main reason I pursued programming past making video games.

I wasn’t that different from other kids. I got really good grades in school and had a social life with my friends. However, I spent multiple hours a day outside of school working on various projects. Even in class, I would always be building projects.

I put the money I made from the app I sold into Cal AI because I knew we had all the pieces for success

My cofounder, Henry, and I started building apps in the summer of 2023. It was just the two of us trying to figure things out from scratch, learning on our own. I messaged some people who built very successful apps to find mentors, and one of our other cofounders was one of the people I messaged. He had previously scaled a couple of apps to a few million downloads, and I had reached out to him for advice. He joined the team.

After that, we started working with a few influencers on videos, and the new app took off faster than any of us could have ever imagined. I quickly became aware that we had all the pieces for success to a much greater extent than any other project I had worked on, and I put the money from my previous app sale into it.

Henry and I spent July in San Francisco working on it, and that’s when Cal AI became more established. We realized this wasn’t just a flash in the pan, but something we could actually scale up.

The most beautiful and proudest moments in my life so far have probably been meeting people in person who show me Cal AI on their phone. It’s awesome to see that something I built is being used by people every single day.

My best advice for starting an app is very simple

My advice to anyone would be to get started. Ignore the noise, ignore the people telling you that it’s impossible to do it at a young age, and ignore the people trying to push you down a specific path to accomplish your goals.

It’s becoming easier and easier to be a founder. There’s a reason the age of these entrepreneurial kids making the headlines is getting younger. I had Google, the internet, and YouTube as my tools, but for the next generation of founders, it’s ChatGPT that they can use to teach themselves. Which is so much easier than watching YouTube videos, where I was limited to the content library that people have posted.

I’m still finding the balance between being a college student and a founder

I just enrolled as a student at the University of Miami, but I’m taking a pretty light course load right now. I’m still working on Cal AI, but I’m no longer needed in the day-to-day operations as much. We’ve put a lot of systems in place over the last year and a half, where I now just have to oversee the vision and guide us in the right direction.

The aspect of college that consumes a lot of time is the social life. The primary reason I’m enrolled in college right now is to meet and socialize with people my age and make friends. This definitely takes up a significant amount of time and mental space. So fun in the short term, but not super productive.

The biggest challenge is finding other like-minded people to relate to. I don’t want to talk about random classes. I want to talk about real-world problems, solutions, business models, and other things that most kids my age aren’t interested in.

Do you have a founder’s story to share? Contact this reporter, Agnes Applegate, at aapplegate@businessinsider.com.