こんにちは。
「姉」は older や big を使って表現できます。
older は「[年上の](https://eikaiwa.dmm.com/uknow/questions/78585/)」という意味になります。
big の方が少しカジュアルな感じです。
【例】
I have an older sister.
「私には姉がいます」
I'm a big sister now!
「私お姉ちゃんになったの！」
ぜひ参考にしてください。
「姉」は「Older sister」、「[妹](https://eikaiwa.dmm.com/uknow/questions/52462/)」は「Younger sister」です。「姉がいます」は「I have an older sister」と言えば良いでしょう。ご参考にしていただければ幸いです。
In the U.S., most commonly we use older to explain a sibling that is older than us. We can also use eldest or oldest to explain one particular sibling that is the oldest of all of the siblings. So if they are the oldest of 4 you can say: :She is my eldest sister. But, if one sister is older than you but not older than the eldest sibling, you can say: She is my older sister.
アメリカでは、年上の兄姉を表す際によく使われるのがolder（年上の）です。一番上の兄姉をeldest またはoldestということもできます。４人兄弟の一番上だとすると以下のように言えます。
She is my eldest sister.
彼女は兄弟の中で一番上です。
しかし、兄弟の中では一番上ではないけれどあなたよりも年上の場合は以下のように言えます。
She is my older sister.
彼女は姉です。
The two sentences you see above are great ways to express that a female sibling is older than you. The first sentence would be appropriate in formal settings, like in the office or in a business meeting. The second sentence would be appropriate in informal settings because of the expression sis(which means sister). I hope these two sentences and this explanation help you out!
The female sibling that is older than you would be your older sister.
The female sibling that is younger than you would be your younger sister.
The female sibling that was born at the same time as you would be your twin sister.
The female sibling that was born from your mother or father, but by a different partner, would be your half sister.
A female sibling that is older than you is called an "older sister". For example, you may say it in the following ways:
-I am much closer to my older sister than I am to my younger brother.
-My older sister is getting married next Saturday and I'm her bridesmaid.
年長の女きょうだいのことを「older sister（姉）」と言います。
以下、例文です。
I am much closer to my older sister than I am to my younger brother.
（弟よりも姉の方がずっと仲がいいです。）
My older sister is getting married next Saturday and I'm her bridesmaid.
（姉が来週土曜日に結婚します。私はブライズメイドをします。）
英語では年上の方の「姉」は「older sister」といいます。
年下の「妹」のことは「younger sister」といいます。
例文：
「私は姉がいます」
→「I have an older sister」
「私は二人の妹がいます」
→「I have two younger sisters」
「23歳の姉と15歳の妹がいます」
→「I have an older sister who is 23 and a younger sister who is 15」
ご参考になれば幸いです。
アメリカ合衆国 
日本 
イギリス 
南アフリカ 
