to understand it? not that long.
to learn it? a little longer.
to really master it? probably several lifetimes ....
besides you will have your own learning curve .... you can be a mediocre coder within 1 year that's rather possible and in 10 years you're probably a decent one.
I am in the second decade, I am a decent one. I understand most concepts, different languages, paradigms, protocols, hardware but I will never finish learning. And if I would I would change my job.