I learned html/design in 98 when I was 18'ish, but I always thought of it as a hobby - not a real career, till web apps and wordpress came along, still I would install wp sites, and do SEO for people but still worked for shit pay and shitty jobs, in 2011 at 31, I started learning to code using MVC frameworks (Ruby on Rails and Laravel specifically), I learned better coding skills, etc...and it's only the past 3-4 years that i've been taken seriously and started being sought after by companies and small businesses for freelance work.

Best advice is just build stuff, and always work on your portfolio and resume. The more you can showcase that you've accomplished the better.