Hi,
According to the eligibility criteria for NEET, you don't need to score 50% marks in each subject in NIOS for NEET. But you need to score aggregate of 50% in PCBi.e Physics, Chemistry, Biology.
Also, to be eligible for NEET,
You need to be atleast 17 years old.
There is no upper age limit to apply for NEET 2021.
And there is no limit for maximum number of attempts in NEET.

You can visit below site for more information,

https://medicine.careers360.com/articles/neet-eligibility-criteria/amp

Hope this information helps.
Good Luck!!!

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