There is no minimum age prescribed as per the CSIR NET. So you need to complete your Masters program or atleast your Bachelors program in order to be eligible for the examination. So you will need this criterions to be satisfied. The upper age limit if 28 years of age with 5 years relaxation for the Females.

To know more about CSIR NET 2021 visit the link below:

https://competition.careers360.com/articles/csir-ugc-net

I hope this answer helps. All the very best for your future endeavors!