I have choosen science stream can I apply for cds.and I was 18now wheather I was able to apply now.

Even if you take Science in intermediate you can apply for Combined Defence Services. The minimum eligibility criteria says that, you must have earned a degree from a Recognized university or equivalent. Only Physics and Mathematics at intermediate is required for Air Force Academy. For Indian Military Academy, Indian Naval academy, the candidate's age must be between 19 to 24, for Officers Training Academy, the age must be within 19 to 25 years, and 20 to 24 years for Air Force Academy. For UPSC CDS, you must complete your graduation first. http://competition.careers360.com/articles/cds-eligibility-criteria