for ISRO: 

eduaction qualification- 

• First class in BE/B.TECH or equivalent in exam with minimum 65% or cgpa 6.84 on a 10 scale.

nationality -  Indian

age limit-  18 to 35 years as on 25/05/2016

for NASA

• Bachelors degree from an accredited institution in engineering, biological science, physical science, or mathematics. An advanced degree is desireable.
• Atleast 1000 hrs pilot-in-command time in jet aircraft. Flight test experience is highly desireable
• Ability to pass a nasa space physical which is similar to a military or civilian flight physical

Hope this will help you.

All the best