You can start sending your CV anytime you want. However, all job adverts require BA diploma and TEFL Cert, both docs. needed for Working permit, which school must get in order to issue Invitation letter.

Once you have WP and Invitation letter, you can apply for Z (working visa) at Chinese Embassy in your country, which is the only proper visa for working in China.

Another requirement is 2-years of working experience, what prevents too young people to apply for jobs at Chinese schools.

Send few CV, and see what response you'll get of Chinese schools.

Legally no but in practice yes. The school can make a fake diploma and CV for you to apply for your Z visa. This is standard practice in China as many teachers here either never graduated from a four year college, aren't native speakers or don't have two years work experience prior to teaching in China.

It doesn't take long to find a job in the ESL/EFL field if you're qualified to teach it. All you have to do is major in TESL or TESOL and the jobs will fall into your lap. 

Yes, those which require only a TEFL.  Otherwise they want to see the actual degree.  No need to get hired early, especially with an appropriate degree.   It's fast.  Just get the other things done. 

Ok - a few things...

Firstly - applying for a job - anyone can do! Any time! At worst, you get nothing. At best, an offer from a real, good, legit school with good pay, in a nice city, etc etc.

Secondly - hiring season won't really start until around late April into May (sometimes later..). Most schools will need to find out if their current lot of teachers are going to hang around or not. Also, getting a teacher in fully prepared, legal, etc takes planning and forethought... something which most lack here!

Thirdly - remember, although you might finish your course in April, you do not officially graduate until the following semester. THAT's when you get your degree! Until that point - between course completion and actual graduation - you are considered a 'graduand'. (technically, they can still withhold your degree for a variety of reasons). You should, therefore, get a letter from the head of department saying you are a graduand, and that your official graduation doesn't take place until later. This could be an issue for some 'real' schools (remember... the crap schools will take anything anytime - cos of the turn-over... is that where you want to work??) so, you won't have a degree to show anyone!!!

Also remember - the semester won't start until September (usually later in September... depends on the year), so if you're looking to work in a university or school, this may make things easier.

If, however, you're looking at a training mill, the July-Sept holidays can be some of the busiest in the year...