Do what you want in the end.
You are so close to a keystone, so you can wait for that if you want. It is a good boost in power but it won't suddenly make you god.
Well if you wait for 18... might as well wait for 20 for runes. There will always be something else to wait for.
If you think you have played bots and learned enough. If you are bored of bots. If you want a real experience. Just play normal games (Or ARAM, ARAM is fun). Even if you lose it is ok, that is your learning time. And playing a real game is completely different from bot games, so do it. Riot's matchmaking should set you up with other new players, it won't always work. But don't let that deter you. Just tell them you are new learning and trying and play (seriously communicate).
Also, I am bad. But when I was level 29 I purposefully didn't use a keystone. I mean I didn't care at the time, the games were just for fun. And some people thought I was still level 17 and such so you can get other advantages.