The first red flag is that they are hiring an 18 year old who seemingly has no bachelor's degree or teaching certification (TEFL, CELTA, etc.). This is illegal in China. To teach English, you would need at least a 4 year bachelor's degree (in any subject, but preferably English or education related) and a teaching certification. Post-graduate work experience is required by many schools as well, but from my observations, this requirement is on a case-by-case basis depending on where or who you are working for. Any reputable recruiter would tell you that you need a Z visa, and nothing less, to work full time in China. It is for this reason that most schools that are certified to hire foreign teachers won't consider hiring anyone younger than 21-23 years old.

Except for: a university degree from any western university is acceptable. For example, a three year BSc degree, called an ordinary degree, from a British university is accepted.

Why is this important? Not only can you be deported, fined, and banned from the country if you're caught working illegally without a Z visa, but companies and schools can, and most likely will, screw you over at their earliest convenience because you DO NOT have a legal contract that can be enforced. There are plenty of stories online of people who were abused and screwed over by their employers because they didn't have a legal Z visa. Believe me when I say you do not want to be one of those people.

What about the job detailed below? Does it constitute illegal employment?

http://www.eslteachersboard.com/cgi-bin/China/index.pl?read=289111