1) I am offered a more interesting position at my current job.
2) I have come to realized that my personalities are more suitable for teaching ESL students than working as a sales man. This is the main condition why I want to come back to teaching English.
3) Personally I prefer teaching English to junior high school students instead of children.
4) Michael is more interested in traveling English than in business English. The purpose he wants to learn English is to become a tour guide.
5) For the current situation, I do not limit my opportunities for teaching job. I am willing to teach English for any age of student. No mater they are youth, adults, or children.
6) I believe I am the best candidate for this position because my background and experience have been preparing me well for this position.
7) I hope I have more opportunities to develop my coordinating skills in these five years. Furthermore, I hope I can become the most competitive player in this team.
4) My sentence in #4 revised to
=> Michale is more interested in travel English than business English. His prupose of learning travel English is becasue he wants to become a tour guide.

1) I am offered a more interesting position at my current job.
2) I have come to realize that my abilities are a better fit for teaching ESL students than working as a sales man. This is the principle reason why I want to resume teaching English.
3) Personally I prefer teaching English to junior high school students to teaching English to elementary students.
4) Michael is more interested in mastering traveling-specific English than in business-specific English. He wants to learn English in order to become a tour guide.
5) Currently, I am open to any teaching opportunity. I am willing to teach English to any age of students. Age does not concern me. (or) It does not matter if they are youths or adults.
6) I believe I am the best candidate for this position because my background and experience prepared me well for this position. (You may want to go into greater detail here!!)
7) I hope I have more opportunities to develop my coordinating skills in the next (?) five years. Furthermore, I hope I can become the most competitive player on or (member of) this team.

2) Realize; salesman (no space); this is the main reason?
3) comma after personally;
4) You might want to change the sentence, as it's hard to understand what you mean;
5) teach English "to" any stage of student; "matter"; they are "young";
I think that's it!
Good luck!