Hello @asif_rahman_joy,
Recently I have to do a similar thing that might help you.
I’m suggesting to define some if conditions for all of the age groups, and summing up at the end of the form.
For example adding calculate questions for your age groups, like if( {age} <5, 1, 0 ) will result in 1 if the age is below 5 and 0 otherwise -which you can sum at the end of the form-
You might want to check these articles:
First article which shows how to create Dummy Questions and the second one shows the form operators
Hope this helps,
https://support.kobotoolbox.org/advanced_calculate.html#work-arounds-for-calculations
