Yes, you can use a 5-year-old cheque book. However, you should be aware of the risks involved with using an old cheque book. The bank may have changed their policies and procedures since the cheque book was issued, and this could mean that the cheque book may no longer be valid. The bank may no longer be able to trace the cheque book if it is used fraudulently. It is important to check with your bank to ensure that the cheque book is still valid before using it.