About I started going to high school (When I started going to High School) >> It's better to construct your title into a complete sentence rather than a phrase 

I'm a high school student and I go to (since you used "I" in both sentences, you can use the article "and" to make it into a compound sentence) school by bus. When I was in Junior High, (you can start this sentence with this to make your readers undertand that you're telling a story from the past) I can go to school for about 15 minutes from my house. I got up at 7:00 a.m. because the school starts at 8:30 am back then. However, eversince I started being a highschool student, I get up by 6:00 a.m. since the bus that I get on every morning comes at 7:02 a.m. It was so difficult for me for the first time because i tend to become sleepy and tired in the morning. But now,  I enjoy watching the view around and I read books while in the bus now.

Notes:

- your grammar is good :) 

-however, your sentence construction becomes redundant sometimes :) 

-please try to review on how to construct compound sentences because they make the paragraph more coherent :) 

- be careful with the words you use and always consult a dictionary if there's a word that confuses you :)

- review on the proper use of your PREPOSITIONS :) they're really important 

-please don't forget to use pronouns in your sentence :)

-good job on your work! :) 

About how I started going to high school

I'm a high school student. I go to school by bus. I can go to my junior high school about 15 minutes Wwhen I was a junior high school student, I used to go to school in about 15 minutes. I got up at 7:00 a.m. because class the school started at 8:30 a.m. back then. But since I became a high school student, I must have been getting up by 6:00 a.m. because a bus that I get on every morning comes at 7:02 a.m. It was so tight a close call the first time for me due to sleepiness and tired. ButAt least I get to I enjoy watching around the street views and reading books inon the bus now.

Great job!

Ana