1. for a year
2. since August
3. for a couple of days
4. since nine o'clock
5. since I was a student
6. for half an hour
7. for months
8. since 1996
9. for ages

Explanation:

• "For" is used to indicate a period of time. It is often used with expressions of duration like "a year," "a couple of days," "months," and "ages."
• "Since" is used to indicate a starting point in time. It is often used with specific points in time like "August," "nine o'clock," "I was a student," and "1996."