can any one interpret with explanation for me ?

Interesting Caselet!

I think the highlight of the problem is " Nobody died"

Which means Age bracket (>50 will always increase)

And if you observe 2016 data of (>50 group) number is 29.

And suddenly in the next year for the same (>50 group), there is jump of two people= 31

This should have come from (41-50 group) who were exactly 50 yr old in year 2016 and became 51 year old in 2017.

I guess that could be a starting point of interpretation.