Hello Hari Krishnan,

I would like to tell you some of the basic eligibility criteria for NATA 2019:

• You must have passed 10+2 exam and scored minimum 50% marks in Physics, Chemistry, and Mathematics and also in aggregate. 
• There is no minimum or maximum age criteria for appearing in the exam.

So you have to pass the 12th Boards so that you can be eligible.

I would suggest you visit the careers360's link given below which has a detailed info NATA 2019 with all the details mentioned.

The link for the same is:https://engineering.careers360.com/articles/nata-eligibility-criteria

Hope this helps and all the best!