Morgan Eckroth didn't buy her first cup of coffee because of the taste or caffeine. She only wanted to show off her new driver's license at age 16, walking down her school's halls with her car keys and a green-accented Starbucks cup.

As many a teenager does, she got hooked. Eckroth, now 24, made $141,000 last year working three jobs — social media creator, marketing strategist and barista — that all revolve around coffee, according to documents reviewed by CNBC Make It.