You can apply aftra or before degree

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To join air force then you will be required to give NDA exam.

You can check the NDA eligibility criteria below:

Age Limit: The upper limit is 19 year 6 months for appearing in NDA.

For Air Force and Naval Wings of National Defence Academy and for the 10+2 Cadet Entry Scheme at the Indian Naval Academy: The candidates must have passed class 12th with Physics and Mathematics conducted by a State Education Board or a University.

There are some physical standards too that you need to Clear. To know Click below Link-

https://competition.careers360.com/articles/nda-eligibility-criteria

All the best.