How I Cofounded a Million-Dollar App With a Teenager; Changed My Life

This as-told-to essay is based on a conversation with Jake Castillo, a 30-year-old cofounder at Cal AI, an AI-powered nutrition and food tracking app, based in California. Business Insider has verified the financial claims mentioned in this artical. This story has been edited for length and clarity.

Right after my master’s, I worked in management consulting, and hated it. I immediately looked for something I’d hate a lot less that would pay a comparable salary.

I joined an AI startup part-time after I saw its founder’s post on Twitter about scaling his business. At the startup, we got a high school intern named Zach. I made it a goal to jump on calls with him and ensure he gained something from his experience.

Zach left the internship to focus on school and his own projects, and I decided I had learned enough and made enough connections that I was ready to leave both my part-time startup and consulting roles and start my own e-commerce business.

Right after I left, Zach called me and asked me to help him with his new app. The first few months were tough, and I remember not leaving my room for days at a time because the work was so intense. However, just a little over a year later, we are generating over $1 million in profit each month.

Immediately, I realized Zach was not your normal 16-year-old

When Zach started working with us as an intern in early 2024, I remember asking my boss what he was going to be doing during his internship, and it sounded like shadowing was the main objective. I didn’t think that was the best way to make it a fruitful experience for him.

I Slacked him to introduce myself and learn what he wanted to get out of this. He was working on side projects and figuring out how to distribute and market those products. We started jumping on calls to talk through what I would do and some processes that he should run through.

Related stories

After two months in the internship, he left to double down on the things he was working on. I wished him the best, and that was the end of it. It wasn’t until three months later that he reached out again. That’s when he asked me to join his new app, and it changed everything.

It was the most important phone call of my life when he asked me to join the team

Zach called me and said he had a new app that was growing pretty fast and could use my help managing it if I was up for it. It was perfect timing. The app, Cal AI, an AI calorie tracking app, launched at the end of April 2024, and I joined as one of the cofounders at the beginning of May.

My role is hybrid, as CMO and COO, where I manage our marketing team and oversee all operations. In the beginning, we were so hungry and obsessed that we wanted to succeed more than we wanted to breathe. I hated the long hours in management consulting, but those hours were nothing compared to what we put in.

I’m older than everyone on the team, and my life circumstances were different. I had expenses, and I was planning on proposing to my then-girlfriend at the end of the year. It wasn’t that hard to budget because, as we scaled, I wasn’t doing anything to spend money. I didn’t leave my room. There’d be days when I realized I hadn’t gone outside all week.

What it’s like to work with a young founder

A lot of people ask me about the founding team being so young, there isn’t a “boss” structure, all of us founders are on equal footing, and there aren’t struggles working with each other. It’s been amazing. What has surprised me most about Zach is how he doesn’t let fear or uncertainty steer him. He trusts his intuition and goes with it.

We’ve grown fast, and I think the biggest key has been how obsessed all of us are with our work. There are Cal AI copycats out there with a very similar product and marketing strategy, but not even a fraction of our success. Now we’re at about $3 million in revenue a month and over $1 million in profit.

I’m making the impact I dreamed of making in my career

It’s really cool that our app has been downloaded by millions, and people are DMing us on Instagram, emailing us, or sending us messages in the app, talking about how they’ve lost weight and how their lives have completely changed since downloading the app.

I can’t even articulate how good it makes me feel, especially because I remember how disenchanted I felt when I thought I was going to make a difference and was reviewing PowerPoint decks. It’s like a dream come true.

You don’t know who in your network will change your life

I always tell people when I talk about how Cal AI came to be, to be nice to everyone, because you never know how that one act of kindness can change your life. I was able to join the Cal AI team just because I sent a Slack message to an intern, because I wanted to ensure his good experience. That simple decision completely changed my life.

Treat everyone as if they were the future CEO of Apple or the next billion-dollar company because they very well could be.

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