Are you allowed to take second year courses if you are in third year? Do med schools/grad schools/people who are reviewing your transcript for admission to a masters program look down on you for this?

Most of the professional schools that I have looked into say that students are encouraged to challenge themselves by taking courses that correspond to their level of studies. But I don't think you should worry about taking one second year course in third year. I think they are referring to the people who try to pick most of their courses from first year courses to boost up their gpa.

For Western Schulich School of Medicine and Dentistry, applicants are required to have at least 3 full courses (6 units) or 6 half courses (3 units) that correspond to each school year. Basically 18 of the 30 units MUST correspond to the year of study; Second year must have 18 units that are second year and Third year must have 18 unis that are third year.

You must also have 30 units to be considered full time by the Schulich School of Medicine and Dentistry.