Dear Student,

Let me tell you one thing, you can give every NDA exam if you are coming between the age of 16 1/2 to 18 1/2, just fill the 12th appearing option in the application form.

But you will only be eligible for SSB if you are really a 12th appearing or 12th pass student.

As now you are in 11th class and you have filled the exam of NDA written, here you will not face any problem till the written examination but if you will be able to clear the exam then they will call you for SSB and there they will ask your 12th class proof, but at this time you don't have any so yes you will not eligible for the SSB. For SSB you need to be either in class 12 or passed the 12th exam.

Best Of Luck!!!