But I saw that there's often no word for 'his', and that's why I thought it should work like this here too.
I'll report it just in case. Whether it gets accepted or not, that one "his" doesn't change the meaning in my opinion.
już can be translated like "already", so my version is " the boy is not already eating dinner"
It can - in a positive sentence. Not in a negative one. So no, your version doesn't work.
What about 'yet'? How am I supposed to know whether a Polish sentence means, for example, 'the boy isn't eating supper anymore' or 'the boy isn't eating supper yet'?
Polish uses the word „jeszcze” for that. So that would be „Chłopiec jeszcze nie je kolacji”.
No, I didn't have an "extra space" in any more, which is correct UK English, whereas anymore (a US American word) certainly isn't.
When can 'juz) (with a dot) mean yet. Yet seemed to me the obvious answer here rather than any more