• I bought the bag last year.

    I bought the bag last year.
  • I started using the bag because I started school.

    I started using the bag because I started school.
    This is my school.
  • Period: to

    I have used it for five months.

    Yes, only for five months, this is why it looks so new.
  • My birthday

    My birthday
    And my sister has bought me a new bag, so I want to sell the old one.
  • It is still in an excellent condition.

    The bag is very clean and it seems completely new.
  • I want to sell it

    Yes, I want to sell it because I have a new one, my sister gave it to me.