How long does it take generally, more or less to learn web development to get to basic enough skill level to make money?

It depends on a lot of factors, your initial skills level, how fast of a learner are you, how much time do you invest in learning and practising, and so on. But I am sure you know that already.

But before I attempt answering your question... Let me say to you that if you are currently on a different career path (have a job elsewhere), my advise is for you to continue on that job to make a living (at least for the time being), while at the same time learning and doing web development on the side. This way, you can build up your portfolio without having the pressure to make a living out of it.

Once you have a decent portfolio, you can then decide to switch your career path by looking for a full-time web developer position. But if you're thinking of working as a freelance web developer, I guess you can try to keep your main job (the one that pays the bills) for as long as you can, this is because the freelance web development work is up and down. You may not have a constant stream of work.

Now, back to your question, "generally how long would it take to get to a decent skill level that I can start earning 30,000 a year from making websites?" A decent skill is relative, but it doesn't take long at all to learn basic web development. What you need to start doing. Build your personal website, your cousin's blog, your friend's site, your dad's business website, etc. In other words, start building as soon as you start learning.