I would encourage you to keep at it. If my colleague is anything to go by marketing people have an interesting skill set which can complement programming skill

I would encourage you to keep at it. If my colleague is anything to go by marketing people have an interesting skill set which can complement programming skills very nicely. Having experience with the business requirements is very useful and marketing requires a lot of people/presentation skills that many programmers don't develop. It will take a long time (years as I said), but you can get there eventually if you want. The best way is to just build personal projects that you actually want. I would stay away from the toy problems after you have a basic grasp of the concepts and just learn along the way. You will need to go back to the toy problems to polish certain skills, but you should finding out what you need to work on from your every day coding. Good luck!