アメリカやほかの国では[小学校](https://eikaiwa.dmm.com/uknow/questions/36103/)が6年で終わりじゃなく、そのまま7-12まで数字が続いていきます。日本でいう[中学校](https://eikaiwa.dmm.com/uknow/questions/42188/)一年生なら7th grade,高2なら11th gradeのように言います。
I am 13 years old and in the 7th grade.
私は中学校一年生で13歳です。
I'm in the first grade of junior high school, and as old as a 7th grade student in the States.
日本と外国では学校の制度が違うので、「[中学1年生](https://eikaiwa.dmm.com/uknow/questions/51004/)」を英語で表す（the first grade of junior high school）と良いでしょう。
その際、関口さんの書かれた通り年齢は7th gradeと同じになるので、
「7th gradeに[相当する](https://eikaiwa.dmm.com/uknow/questions/59320/)」と言い添えるのが理解しやすく親切だと思います。
In the States, or at least in Texas, we don't call junior high school students by 中1, 2, 3.
Instead, we say the grade year. For example:
- 中1 = 7th grade
- 中2 = 8th grade
- 中3 = 9th grade
For your self-introduction, you can just say:
- I'm in 7th grade.
Depending on your school system, the first year of middle school (also called 'junior high school') will vary. Some students start middle school in 5th grade, some start in 6th or 7th grade, whatever grade you start at in middle school, you can explain that you are now starting middle school by saying:
'I'm in my first year of middle school'
This is a good way to explain that you are just now starting middle school.
" Hello, my name is ____.
I am ___ years old and in my first year of middle school.
In my free time I enjoy to do_____. "
学校にもよりますが、"middle school/junior high school"(中学校)の最初の年は変わります。小学校5年生が中学最初の年にあたる人もいれば、6年生や7年生が中学一年生にあたる人もいます。あなたの言う中学一年生が小学校でいう何年生にあたるのか分かりませんが、中学生になったばかりだと言うには以下の表現が妥当でしょう。
"I'm in my first year of middle school."
(私は中学一年生です。)
これは中学校に入学したばかりだと説明するのに良い表現です。
"Hello, my name is~."
(こんにちは、私の名前は～です。)
"I am~years old and in my first year of middle school."
(私は~歳で中学一年生です。)
"In my free time I enjoy to do~."
(暇なときは~をするのが好きです。)
"I'm a 7th grader.."
This would be an appropriate explanation if you are speaking to someone who understands the schooling system in your country.Some countries don't have a "middle school".
"I am currently my first year of middle school"
This is also a good way to explain your current level of school to someone you were having a conversation with.
"I'm a 7th grader."
あなたの国の教育課程を知っている人に言う時にふさわしい言い方です。"middle school"(中学校)が無い国もあります。
"I am currently my first year of middle school."
(私はいま、中学校の一年目です。)
話し相手に自分がどの教育課程にいるのかを伝えるのにいい方法です。
You are in your first year of middle school, and wish to explain this in your self-introduction.
In that case, you can try one of the above-suggested example sentences which may be appropriate for any given situation. There are always a variety of ways to respond to someone or make a comment - depending on the context and other factors such as nationality, appropriacy and body language.
In Japan, I am in the first year of middle school. This is the same as being in 7th grade in America.
In America middle school starts at 6th grade, but in Japan middle school starts at 7th grade. So I am in 7th grade, but it's only my first year of middle school.
In Japan, elementary school is from kindergarten to 6th grade. Middle school is from 7th grade to 9th grade. High school is from 10th grade to 12th grade. I am in my first year of middle school so I am in the 7th grade.
In Japan, I am in the first year of middle school. This is the same as being in 7th grade in America.
In america, the first year of school is called kindergarten. People enter kindergarten at age 5. Then they go to first grade the next year at age 6. Then there is second grade, third grade, fourth grade, and fifth grade is the last year of elementary school. Middle school starts at 6th grade and 7th grade is the second year of middle school. Middle school ends after 8th grade. Then high school is for four years from 9th grade to 12th grade and most people graduate at 18 years old.
In America middle school starts at 6th grade, but in Japan middle school starts at 7th grade. So I am in 7th grade, but it's only my first year of middle school.
This is the short answer to help Americans understand that in Japan middle starts on year later than American schools.
In Japan, elementary school is from kindergarten to 6th grade. Middle school is from 7th grade to 9th grade. High school is from 10th grade to 12th grade. I am in my first year of middle school, so I am in the 7th grade.
This is the long answer to help them understand Japanese school years in American terms.
The education system differs in every country. In the USA and Canada, secondary education is referred to as High School. In Ireland, it is called secondary school and it lasts for 5 or 6 years, depending on if you choose to do an extra optional year, called Transition Year, after the first three years. Students are generally between the ages of 12 and 18.
"I started secondary school this year so I am in 1st year"
"I am in 5th year. I have one more year left before I graduate"
You can use these two phrases interchangeably to have the same meaning. Although very similar in sentence structure, the first one describes what level you are at within a certain school such as, "middle school." In the second example, you are referring to what grade you are overall regardless of what level of school.
When wanting to tell someone that you are in the first year of junior high school say;
- I am in 7th grade.
- I am in the seventh grade.
- I am currently in my 7th year.
アメリカ合衆国 
日本 
南アフリカ 
イギリス 
アイルランド 
