Do I need 4 years experience before being able to write the CISSP exam?
You can take the CISSP without the experience, however, you will not be a CISSP until you can prove the experience which is five years or four years plus 1 year for a degree.
If you took the exam and passed without the appropriate experience you could become an associate of (ISC)2.
You can find more information at these sites:
Also, there is a time limit to getting the experience.
As I understand it, you have 6 years (required years of experience +1) after passing the exam to get the experience.
This is not surprising. ISACA allows you to take their exams without the experience. You just have 5 years to get it for their certs.