is it a proper answer? whether on grammer or meaning?

Compared to other people, and no matter what you have to sell ?an idea, product, or project proposal, how would you rate your selling ability? Please mark one and briefly explain in the space provided below why you chose that answer.
Top 10% Top 25% Top 50% Bottom 50% Do not know Please explain your answer briefly:

A: 10%. I had three impressed successful experiences when I was 8 years old,14 years old and 20 years old. I am good at understanding what customers really want and always have a persuasive way of talking.

I would not use the word impressed there. Just "successful experiences" is fine. (And the word you're looking for is "impressive", anyway.)

I don't know that this would be a good answer for what I assume is a job application for a sales position. If you've only had three experiences of selling things, and two of them happened when you were a child (and presumably not in a work setting), A) those would not be terribly relevant to a prospective employer, B) they would certainly not put you in the top 10% of salespeople, and C) the answer is extremely vague and unhelpful to an employer. You need to cite more specific examples of your skills and technique.

it's very kind of you to give that suggestion. I made a revision as follows. Could you give more correction?

I sold the Welfare Lottery when I was in middle school. My sale was 4 times more than the average. It makes me more enthusiastic about sales.
Intern in GIORDANO clothes store. Made the biggest sale among 20 interns, even bigger than some employees.