Is this exam difficult for person who has hands on experience with Apex & VF for 6 months ?
The Platform Developer exam covers a broad range of topics on developing for the Force.com platform. You'll want to read the study guide to see everything it covers. No only do you need to be proficient in Apex and Visualforce, you are expected to understand data modeling and the technical architecture of the platform. You'll need to understand testing as well as common tools used for developing on the platform.
Only you will know if the exam is difficult for you. Evaluate the study guide and then decide where you need to learn more and where you feel comfortable. If that second category is at least 80%, you should be good to go.