Question about CBSE 9th registration

As per the guidelines of the central board of secondary education (CBSE) the minimum age to appear in the 10th board exam is 14 years, as of 31st December of the year of examination.
So for 9th class, it should be one year less. If your son wants to register for 9th class that is 2020, he should complete his 13th year by December 2020.
Your son's date of birth is 11/12/2007. He will complete his 13th year by 11th December if 2020. So he can get registered for this year. Let him go ahead.

As per CBSE guidelines a student should attain a minimum of 15 years of age while appearing for the class X examination. By reverse calculating it amounts to completion of 13 years and a few months at the time of admission in class IX. For sake of simplicity it is taken 13 years and 6 months for admission in class IX which in another way can be said as attaining 14 years by December of that particular year.

Your son's DOB is 11.12.2007 and he would be completing now 12 years and about 7 months so he is falling short of age by almost 11 months. You have to check with the college as sometimes the principal has also some power to relax age to certain limits (up to a maximum of 12 months). Once that is clarified you can proceed ahead.

As per CBSE guideline, the minimum age to write class ten Board Examination is 14 year as on 31 st December of the year when he is to write the same. The registration procedure is to take place just a year back of the normal examination schedule, hence on 31 st December 2020, he should have completed at least 13 year. Since the date of birth of your son is 11. 12. 2007 and upon calculating his number of years on the 31 st December 2020, he will be 13 years 19 days making him entitled for Registration- procedure for the said examination.
So your son must go ahead with the formal procedure of the said examination.