I'm 19 and want to build a startup eventually. What should I learn first? (I will not promote)

19, no degree and my long-term goal is to eventually build an internet business/startup. Right now I'm trying to figure out what would be the highest-leverage way to spend the next few years learning. I'm considering getting into tech sales as an SDR, where I'd learn prospecting, cold calling, discovery, understanding customers and how companies actually buy. Another path I'm considering is GTM/revenue engineering, where I'd learn outbound systems, data, automation, AI tools, CRM and the systems behind acquiring customers. But I'm wondering if I'm overthinking the job title. If you were 19 and knew you wanted to build a startup eventually, what would you deliberately try to become really good at before starting one? Would you focus on: - sales and customer acquisition - coding/product development - marketing/distribution - working at an early-stage startup - learning operations and business fundamentals - building small projects on the side - or something else? I'm less interested in "become an SDR" vs "become a GTM engineer." I'm more interested in what skills and experiences actually compound when you eventually become a founder. Would love to hear from people who have actually built startups and what they wish they had learned earlier.