For CTET Paper-I (classes 1 to 5), you need senior secondary with 50 percent marks plus a D.El.Ed or equivalent teacher training.
For CTET Paper-II (classes 6 to 8), you need a graduation degree plus a B.Ed or equivalent.
Final-year teacher-training students can usually apply if they complete the course by the cut-off date in the notification.
There is no upper age limit for CTET.
The CTET certificate is now valid for life, so qualifying once is enough.