Yes, you can!
You can add subjects from any year group or level to your account, regardless of the year or level you selected. Great news, right?
It's pretty easy to do. Just head over to your account settings and follow the steps for adding or changing subjects here: How do I change or add subjects to my account?
PS. The maximum subject selection limit applies across all year groups, not per year group!
Please note: If you are a student on a school account, your school will have to add you to a class to access a subject, so you may not be able to access subjects across multiple year groups in that case!