Most startup advice is also good advice for 20-somethings. Get to an MVP quickly: Find a way to practice your target profession as soon as possible. (Don't spend hundreds of thousands getting a law degree just to discover you hate the actual work.) This is easy for programmers: just start building stuff before applying to the CS program. After MVP, iterate quickly: So you know Ruby? Time to learn another language, or…
From a purely financial perspective, money now is better than money later though. A 20 year old who secures a job that nets him enough to save $15,000 per year until retirement will ultimately have a lifetime net savings of about the same as someone who finally finds a job that pays enough to save $50,000 per year at the age of 40.