The minimum eligibility criteria for appearing the paper of CDS exam 2020 as per the rules of UPSC are that-
1. The person should have age ranging from 19 to 24 years
2. The person must be a citizen of India
3. The person must have completed his graduation.
So, the percentage of 12th doesn't matters. The only thing is that you should satisfy the above minimum requirements.
For more details about CDS exam, you may visit the link given below:
Best wishes for your future.