Age criteria for admission into Class 1

The criteria of age for admission into class I in CBSE is as follows.
The minimum age should be a minimum of five years as on 31st March of the year in which the admission is requested.
The maximum age should be 7 years as on 31st March of the year in which the admission is requested.
You boy's Date of Birth is 20th October 2014. His age on 31st March 2020 is 5years 5 months 12 days. So it is more than the minimum age and less than the maximum age. So there will not be any problem. You can admit him.

Whereas the minimum age is 5 yrs and 8 months as on 1st, June of the admission year in 1st std. But your son will be completing 5 years 8 months by June 20th, but not by 1st June. That may be the reason they rejected in ICSE schools.

You can go ahead and admit him in CBSE schools.

Since your son is covering the age criteria fixed for class one in CBSE standard, the minimum being 5 year on 31 st March of the year when admission is to be sought and the maximum age for admission on the same date should not exceed 7 years.
Hence his age range is matching for admission to class one of CBSE standard and you should go ahead for the admission procedure.
You should not be afraid of reverting your son to class UKG in any circumstances.
In the ICSE pattern, the basis of consideration of age is computed on 1 st June of the year when admission is to be sought and on that day there is minor shortfall of attaining the eligible age set for admission, the same being 5 year 8 month and hence he may be disqualified for admission in the ICSE syllabus.

As we know that we have many boards in our country for education and the most common are the State, CBSE and the ISCE. Every board has their own age criteria and I would like to put in board wise for more clerification.

State Board: When we talk about state board, every state has their norms and we need to follow as per the residing state. As you are talking about Pune - Maharashtra, the Maharashtra state government has fixed the age criteria for the academic year 2020-2021 as follows and the cut-off date is taken as 30th September 2020.
As per the Right to Education (RTE) Act and Education department director Dattatray Jagtap he has asked every board and schools to follow a uniform cut-off date of i.e. September 30 for admission process.
As per the request, the minimum age for admission to Ist Std. is 6 years. If one follow the below criteria, their children or ward will be in the correct age and in the correct class or standard.
3 years - Nursery, 4 years - Jr Kg, 5 years - Sr Kg and 6 years - 1st Standard.

CBSE Board: As per the rules framed by The Central Board Of Secondary Education (CBSE), The cut-off date for the admission to any class is taken as 31st March. Now according to their admissions rules, a child should have completed the minimum age requirement of 5 years or the maximum age of 7 years inorder to secure admissions into class 1 in CBSE board school.

ISCE Board: The Indian School Certificate Examinations (ISCE) has the cut-off date 1st June for the admission. For admitting a child to Class 1, he/she should have completed 5 years and 8 months as of the cut-off date. As per the given DOB of your son, he completes 5 yrs, 7 months and 11days only as of 31st May 2020 which falls short as per the ISCE admission rules, thus the ISCE board school has declined his admission for Class 1.

The age for admission to class 1 is viewed differently by different central boards and state boards but the basic premises is that student should complete 5 years for that. For example in Maharashtra the state has fixed the cut off date as 30th September, 2020 and requires that the student should complete 6 years by that date. It means that student would be above 5 years at the time of admission as usually admissions would be in April-June months.

On the other hand CBSE requires that a child should be completing 5 years by the 31st March of the year in which he is taking admission in the school. In your case the child is fulfilling this condition so you can try to get him admitted in CBSE school.

Earlier, there was a general rule that for admission to class 1 the child should have an age of 5 years in the month of admission which used to be mostly June month of the year. Gradually different boards and state education department started to fix their own regulations in this matter. Though the age is still near that but there are some differences in calculating and depending on in which type of board one is seeking admission it changes. For example in CBSE the cutoff age of 5 years is calculated as on 31st March of the year of admission. But if it is a state board school then one has to find out the exact cutoff date from the concerned school or information provided in the board site. So, you have to calculate accordingly and take a decision. Once admission is provided in class 1, then there is no reason why the child would be downgraded to UKG.