In China, all the kids have to learn English when they were very young.
--> This sentence should not be in the introduction. In your intro, you should papraphrase the topic and state your opinion.
Some experters
there may exsitsexist
such as whether is reasonable
--> What is "reasonable"? I don't get what you mean here.
we all knownknow
understand the outside subjects in his or her owna different language
In a word, I reclaim my point, one of the benefits you learned foreign language at young ages is you can connect the images with the language itself, regardless of one's mother language. That is very important point for language learning.
--> This conclusion is not relevant to the topic. The topic asks whether the advatages outweigh the disadvantages, not what is the benefit.
It is extremely important that everything you write is grammatically correct. If you make grammar mistakes, it will not only prevent readers from understanding your essay but also lower your band score.
Also, don't use rhetorical questions ("So when is the most appropriate time?Begin with the primary school or when they are getting older?", "Why?", "What can we see from that?") too much in your essays.
Best