IMPOSSIBLE !!
There is no possibility to enter into the field of civil services after 12th and through NDA because the age limit for NDA should lies between 16.5 to 19 years and therefore your age is not acceptable so you have to try through another UPSC entrance exam.
There are lots of entrance exams which is taken by the UPSC for the civil services so you can try through another but through NDA ;it is impossible.I think the CDS (Combined Defense Services) which is taken by the UPSC is also for the civil services so you can try for it.
But the thing is that your age should lies between 19 to 22.5 years.And you should be graduate because only the graduate students can apply for CDS.
Thank u!!