Hello dear, 

Yes you can give CPT after 12th. The eligibility goes as follow:

• Candidates must have passed 12th standard from national or state recognised board of secondary education in India.
• Candidates must have registered/switched over to common proficiency course with board of studies of ICAI on or before june 30, 2017. 
• Candidates cpt registeration must not have expired. 
• Candidates applying for CA CPT 2018 june examination must have a valid Id as at the time of filling application form. 

I hope this will help you. 

All the best!