Prior to 2016 - 17, the criteria for admission in CBSE pattern for LKG, UKG and Class 1 was 3.5 years, 4.5 years and 5.5 years respectively as on 1 st June of the same year.
However, this has been revised upward with the increase of four months as on 1 st June from 2017 and onwards.
While computing the age of your son on 1st June 2020, he will be 5 years 7 months and 18 days where as he should have been 5 years 10 months on the said date. Though the shortfall is very narrow and the same can be compensated with the fresh circular if floated by the CBSE Board.
In this context, you may meet the principal of the school to fix your doubt relating to his age.
Of course, the intake of students in respect of age varies from school to school. Hence get your doubt clarified by him. Prepare your son for the written and oral test to be conducted by the Admission - commitee.