あなたが14歳のときに妹の2倍の年齢だった場合、それはあなたが14歳のとき、14 * 2 = 28歳だったことを意味します。
今、あなたの妹は14歳なので、あなたは28 + 14 = 42歳です。
If you were twice as old as your sister when you were 14, that means when you were 14, you were 14 * 2 = 28 years old.
Now, your sister is 14 years old, so that means you are 28 + 14 = 42 years old.