"The younger one is my teacher."
That's the difference between saying "the young one..." vs "the younger one...". The latter is what the English said, but it's a subtle difference in meaning
There are always different ways of saying the same thing, that's why i like to read these comments. I answered without the 比较. Just have to think about what they are looking for i guess. Here is another possibility: 年轻的那个是我的老师。
That's right, but usually it would be 那位 instead, since 那个 makes it sound less respectful, and teaching is traditionally a highly respected profession