hello,

Eligibility criteria Combined Defence Services Examination ( CDS Exam ) are: The exam is conducted by twice a year.

• The one who have settled in India permanently can apply for CDS Exam.
• He  must be graduate or at least appearing in the final year/semester.
• The minimum age limit is 19 to apply for the exam. (https://prepp.in/cds-exam)
• Women students are only eligible to apply for OTA.
• Unmarried students should not be divorced.
• B.tech students can apply for IMA, INA AFA also.
• They both male and female must meet the physical standard specified by UPSC.

Yes you are eligible to sit in the exam only if you are in your final year of Btech.

If you are studying in the final year/semester degree course are required to submit the authentic certificate of passing the degree issued by the University/College at the time of the SSB interview. The certificate of the Degree should contain the date of issue and the date of issue must be before the specified date declared by UPSC. Otherwise, their candidature will be canceled.

https://competition.careers360.com/exams/cds

hope this helps!!