When are you ready? That's not something anyone can answer for you. But take into consideration things that cailano and Vladim above have said (and probably several things others will say following). Play a few games and get the feel for how it works. I hope you are able to get into some successful games by different GMs so you can see how they handle it. If you get into failing games, take note of things that probably made the game fail so you can hopefully avoid them.
There is a certain amount of 'creative endurance' that you have to have to GM a successful game. When you as a GM lose interest in the game, a batch of players lose out who might have really enjoyed the game. If they are playing, they are probably enjoying it. Most players will drop out (sometimes ghosting) when they lose interest so its important to me, at least, to not do that to them. In that, I don't jump willy nilly into GMing an adventure. I kick it around in my mind over and over (usually a few at a time) to try to decide if I really want to run it... and by 'really want to run it', I mean, for me, can I still be excited about the story five or six years from now. Of course I've had games die on me as a GM, rarely less than six months into it. I've only ever just abandoned one game and that was because there was a lot of conflicts between several different players. I told them I was closing the game. Conversely, I've GMed one game for 12 years on PbP and another for 8 (my two most successful ones) and a couple more for 5 years. I'm not a great GM, but I love telling a story and most players are pretty forgiving and, as long as you keep going and trying and owning up to your failings, they'll usually support you. The point of me bragging about mentioning my longer running games is to show what I mean by 'really wanting to run it' (mentioned earlier). Its hard to keep that kind of enthusiasm, but if you do, and you have good players, they'll have it too, and it becomes a lot of fun.
That's not to say that every adventure you might GM needs to be a decade long experience. If you want to do a short game, say so. Just let everyone know its intended to be short and sweet (bloody? exciting? whatever). People can get behind that too. In fact, some people might be looking for a "one off" so they don't have to commit to some epic yarn.
I think as a New GM and someone new to RPG, be sure to also tell that bit of info. That helps players be 'more forgiving' because they have better knowledge of what they are getting into. Someone who doesn't want to help you learn, simply won't apply for your game. No harm, no foul.