Age criteria for 1st class of CBSE

As per CBSE norms, A child is eligible to get admission in class 1 if he/she is a minimum of five years of age completed as on 31st March of the academic year. As mentioned above, Your son's dob is 11 June 2016. Your ward's age is falling short by 3 months. So, you are eligible for UKG. But, many schools give exemption regarding age. So, once you should contact from school management.

For admission to class 1 the CBSE eligibility requirement says that the child should be at least 5 years and 6 months old as of 30th June of the academic year. As mentioned by you the DOB of your son is 11-June-2016 which means that he would be completing only 5 years and about 20 days by 30th June 2021. So, it is clear that he is falling short by about 5 months and a few days. If it is only a difference of 30 days or so sometimes the principal can give special exemption but here in this case the difference is too much.
On the other hand for admission to UKG (CBSE), the prescribed lower age limit is 4 years and 6 months as of 30th June of the academic year. So, you can get him admitted to UKG accordingly.