The English translation doesn't really make sense. Is there a Russian aspect to the meaning that is lost in translation, or does it sound equally to Russian speakers?
I'm not sure what's wrong with the English version, but the Russian sentence means that the teacher is an old man.
I think he means the use of "already/уже" here. It is unlikely that someone would use this word here in English, but is it perhaps more likely in Russian?
Why is старый not in the short form, i.e. стар?
Можно и стар, и старый. Абсолютно равнозначно