I think max age should be at least 30-32 years.Because due to this age many of the students don't try to achieve higher education & they apply for CSS and some of them eventually pass it.But they are unable to do good sometimes due to lack of knowledge.If they are able to have time for higher education may be they are able to serve more.A Master or M.Phil degree holder is definitely better performer(In my point of view).

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Lord grant me strength to change things i can courage to accept things I can’t & wisdom to know the difference