introduction

Hello everyone.
I'm Youta Kawanishi.
I was born and had lived raised in Yokohama, for which is where I graduated high school.
Now, I live in Tokyo.
I have learned English since when I was started learning English in junior high school student but when I compared to then and now and I was 12, I think my English skill doesn't hasn't changed.
I want to improve my English skills and tell talk to each other about our native languages.
Nice to meet you. Thank you for reading.

Ryan's corrections are generally good but this sentence is problematic:

"I have learned English since when I was junior high school student but when I compare now and I was 12, I think my English skill doesn't change." 

The correction "I have learned English since I was a junior high school student but when I compare myself now to when I was 12, I don't think my English skills have changed" is both a run-on sentence and has verb problems ("have learned" doesn't make sense). Better alternatives are:  
- I have been learning English since I was a junior highschool student. However, when I compare myself now to when I was 12, I don't think my English skills have changed. 

- I have been learning English since I was a junior highschool student. However, I don't think my English skills have greatly improved since then.

- While I have been learning English since I was a junior highschool student, I don't think my English skills have greatly improved over the past 10 years. 

Introduction

Hello, everyone.
I'm Youta Kawanishi.
I was born in Yokohama and lived there until I graduated from high school.
Now, I live in Tokyo.
I have learned English since I was a junior high school student but when I compare myself now to when I was 12, I don't think my English skills have changed. 
I want to improve my English skills and tell each other about our native languages.
Nice to meet you. Thank you for reading.