There's so much to learn--it's not just how to build cabinets but how to find clients, how to set up billing, how to deal with customers, and more. Until the 1950s (and perhaps more recently) it was common for someone interested in a field to become an apprentice to an older craftsman who already knew the business. I still think this is a good practice.
My recommendation is you find a local firm to hire you part time or even as an intern so you can learn the business from the inside. Spend 10 years becoming the best employee for another firm and then spend the rest of your career selling your skills for your own firm.