Most of the queries are already answered very well. Here I like to add a little more that according to the CBSE age eligibility criteria, a student must be 13 years old or above as of 31st March in the year in which he or she seeks admission to Class 8th. Based on your son's date of birth (29/04/2011), he will be 12 years old as of 31st March 2023, which means he will not meet the age eligibility criteria for admission to Class 8th in the 2023-'24 session.
However, CBSE rules do allow for exemptions in certain cases, such as when there is a delay of up to one month in the student's date of birth. In such cases, the school principal has the discretion to allow admission based on the student's performance in an entrance exam and other criteria set by the school.
Therefore, you should contact the school where you are seeking admission for your son and inquire about their specific rules and policies regarding age exemptions. They will be able to provide you with more information on the entrance exam, eligibility criteria, and any other requirements that need to be met for admission to Class 8th.
"Education is the passport to the future, for tomorrow belongs to those who prepare for it today." - Malcolm X