Mr. Vasu, you should put this in a new thread as it has nothing to do with the original query.
In any case, the question is whether he had a service break or not when he was absent for 100 days.
If not, then you need to see whether he worked for 240 days in the years (his leave is broken into 2 years I think, so he probably did 240 days in each year) including his paid leave.
For that matter, I think even LWP if it was approved will count as days worked (but I am not sure)
he has worked with you for 35 years. Do you really want to be petty and deprive him of 15 days pay?
I think by law he is entitled to count his current year in gratuity calculation has he has worked more than 6 months in this year.
The question is whether any previous year he worked less than 240 days