Yes, indeed this sentence is just as correct: "είσαι ένα αγόρι" in fact even "ένα" is not needed. So, we're left with: "είσαι αγόρι" :-) We kept it a bit closer to the Eng. at the beginning but of course there are alternatives as you suggest which are accepted. Thank you for your input and please send more it helps to improve the course.
Εσύ είσαι ένα αγόρι > Es(í í)n(e é)n(a a)góri. It seems to happen very often in languages with that type of words, you know, these that starts on a vowel and end in another, pretty like Spanish, take an example in this: Este estudiante está haciendo otro horario. That almost never happens in English.
so it's είσαι for the second person and είναι for first? what are all the different variations on "are" depending on who is speaking? I thought the -εις ending was for second person and -ω for first person? Or is there not much consistency in the suffixes, and it varies from word to word?