Ok right, so I have attempted to answer the questions and the reasons why a student learning English would make them. Would anyone be able to look over them and tell me if I'm on the right lines or where I am going wrong. I hope this is acceptable as it is not anyone that is telling me the answers but rather reviewing and guiding me on areas that I may have missed. The numbers refer to the corresponding questions;
1) The mistake here is 'since', it should be 'for'. In a language like French, Depuis means both for and since, so when learning English there can be confusion because both have different connotations.
2) I would say that this needs to be "It's high time we finished this" referring to the past tense. There is often confusion when learning English between referring to present and past tense.
3) I think the error here is referring to both past and present tense in the same sentence. Again, grasping tense is one of the most difficult but important things to learn within the English language.
4) In this sentence the error is the adjective; 'attractive', this description is not appropriate in this sense. It appears the speaker has confused the definition of attractive with the adjective 'nice'.
5) 'There' refers to plural, so in this instance it should be "There were far less people at the match than I expected" The confusion here lies with singular and plural reference.
6) I believe this should be "If I were you, I'd get more sleep". The reason for this is that the speaker should use a subjunctive; 'were' instead of an indicative; was, to represent an act of possibility rather than as fact.
Retired English Teacher