When you hear “worm poop made him millions” you are left thinking two things. The first is, “Wow!” The second is, “Yeah, it’s simple, but I probably never would of thought of using worm castings as a natural fertilizer….” But Tom Szaky, in a tale of true entrepreneurialism, did. And in 2001, he dropped out of Princeton to build this eco-friendly business he named Terracycle.

When we spoke to Szaky three years ago in our first Young Guns segment he was already making more than $6 million in revenue annually. True to the company’s recyclable premise, the product was sold in used soda bottles, and it made its way onto shelves at big-name stores like Lowe’s (LOW) and Home Depot (HD). Terracycle was also just starting to branch out into creating other products from waste, from backpacks made from chip bags to totes made from Capri Sun juice pouches.

This September we went back to talk to Szaky about his progress—and from our estimates, it’s been pretty substantial. The company has more than doubled its revenue and has continued to expand the scope of the business, partnering with brands like L’Oreal, Nestle and SC Johnson to run a recycling network worldwide that collects waste that Terracycle transforms into products.

In the last three years Terracycle estimates it has collected more than two billion pieces with 14 million people worldwide participating. Yet, despite the growth, Terracycle’s path hasn’t been completely paved in recycled gold, there’s been some bumps, including three failed retail stores.

Watch more for lessons learned from Szaky

Christina is on Twitter @ChristinaScotti