After reading your question, I checked out various sources to see whether the CBSE board has set any rule regarding the minimum age for appearing in the board examination. I have never heard of such a rule that a candidate has to pass the qualifying class or the previous class with such and such age so that he or she can appear for the 10th standard board examination. In fact, I passed class 10 at an age younger to the average age of candidates appearing or passing class 10 examination that year.
When I checked up, I was astonished to see that many are saying that the age of appearing the board examination of class 10 under CBSE board is 15. That means, while taking admission in class 9 you must be of 14 years of age. But certain cases were also reported where candidates appeared in class 10 examination but being of 14 years of age.
To clarify this, I looked up the official website of CBSE and there I saw that there is NO restriction of the age of a candidate appearing in the board examination of class 10 under CBSE board. They have strictly mentioned this under the rule 15, that a candidate becomes eligible for the board examination by virtue of the following:
- A candidate should have passed class 9 with satisfactory aggregate and 60% attendance
- The candidate should have passed the selection test of class 10.
- The candidate must possess minimum 75% attendance in class 10.
If any candidate meets these criteria, then no school has the authority to reject that candidate's application for appearing in the board examination of class 10. Age is not a bar for the right candidate appearing in the examination. So do not worry and let your cousin go ahead for the CBSE examination. No special permission will be necessary.
If age would have been a restriction, then I would not have been able to pass graduation at a tender age of 20 years.