Regarding my son's admission to LKG or Nursery

It is better to put your kid's into LKG next year and kid seems completing 3.6 years old as well. Few schools' stage, like, Playschool, Nursery, LKG and UKG etc., few of them are, Preparatory class (pre-nursery), Nursery, LKG and UKG, and, few, Preparatory, LKG and UKG only. State board, ICSE, CBSE and other private board differs.

When you put him/her in LKG then his/her age will be 3.6 years (though looks little burden of the subjects and preparation etc.) and when he completes UKG then his/her age will be around 5.6 years old to get admission in 1st standard / grade. This will be helpful per age and 5th standard in or around 10 years old etc.

As far as age is concerned a child should complete a minimum of 5 years and 6 months when he is getting admitted to 1st Standard. Now your son is 2 years 6 months. When he completes his 3 years and 6 months, he should join LKG. Then he will be competing for 4 years and 6 months when he will be in UKG. Then he will be completing his 5 years 6 when he is in 1st class. So next year it is better to admit him to LKG.
It is very difficult for the kid to cope with the class if we put him in LKG when he is around 2 and a half years only.

As per CBSE rules, the minimum age for admission into LKG should be 3 years and 6 months. As mentioned above, now your son's age is 2 years and 6 months. So, it would be better to admission into LKG next year because he will be completing 3 years and 6 months till then. And he will fulfil CBSE age criteria. When your son will join 1st standard till then his age will be completing 5 years. And as you know, the minimum age should be 5 years for getting admission into the 1st standard. Almost all boards demand the same age for 1st standard. If you get admission into nursery next year then your son would be one year back from the same age group children.