1) What do you mean by "good handling." I was able to confidently do my work after a few weeks. I was able to confidently troubleshoot after about 8 months. I've been using it exclusively for 3 years now, and my general knowledge of the system is just as good if not worse than it was after 8 months. I found that when everything in Linux was new, I devoured the knowledge like a hungry hungry hippo. I knew Debian inside and out. Then when there was nothing left to learn that held appeal to me, I started branching into other things like development of apps, etc... I'm still learning that kind of thing every day. So in short, 2 weeks to get your work done (probably less nowadays with all the modern fancy distros out there), 6 months to get to know the underlying system.
2) I started when I had just turned 18.
3) Does HTML count? If so, then it's HTML. If not, C++.
4) If we're talking HTML, I learned enough to hack together your standard webpage in 2 weeks in the summer before junior high. However, HTML is a markup language and dead simple to boot. My first real programming language was C++, taught to me through my university (yes, I had never even seen programming languages before I came to university as a computer engineer! Thanks a lot, high school!). Again, it depends on what you mean by "good handle" on the language. The class lasted one term (4 months), and by the time we finished I was as fluent as a new programmer can be expected to be (confident with concepts like abstract classes/virtual functions, templating, inheritence, static members, etc... but without much experience to know how these can be useful).
5) It actually took me longer than I would have liked. I wanted to get involved after my first year of using Linux, but I didn't start doing much 'till after my second year due to just being too busy. So it was a little past my second year mark when I started learning code in earnest. I still am not affiliated with any specific project, but have done patches here and there for various Gnome programs.
What's this survey for, anyway?