Is the code meant to be pure product code? If so then you could at least maintain that as a side project of a given level of commitment per your own specification, and see how it goes--there's the meat of discovery for you in this kind of situation.
And despite your question being kind of specialism-focused, your actual experiences already show sustainable energy is available for you as applied toward a broad approach to a variety of skills, rather than a specialized approach. This can be really helpful to consider.
For related reasons, I'd almost hesitate to recommend even answering your original question. I'd rather recommend questions like: When and how much to learn to code; What kind of code to write; What kind of code best supports my goal for this month; etc.
Similar with marketing, sales, and design. At 21 you should be able to leverage huge swaths of time toward learning a variety of things, and understanding their value as expressions of who you need to be in given contexts.
The result should be a more nimble approach toward your personal & career decisionmaking, with enough of a foundation to shift your perspectives between specialties as required to support your interests as they develop into firmer paths and more specific opportunities.
Just some thoughts though, good luck.