Hey as per my idea no you cannot join ISRO After 12th and here I am giving you its details
Eligibility criteria

Nationality
Candidate should be Indian

Qualification
Candidate should have bachelor degree from recognised university in given stream
Scientists/Engineer 'SC' - Electronics.
Scientists/Engineer 'SC' - Mechanical.
Scientists/Engineer 'SC' - Computer science.

Age limit
Candidate should be between 21 to 35 years

Age relaxation
OBC +3 years
SC/ST +5 years on Upper age.

Selection criteria
Written test
Interview