How to count exact text string matches when there is a partial text string overlap, such as counting both pills and pillaged pills but not pillaged

I am flummoxed but confident there is a way to do this. I just can’t see it.

I want to count the number of class options for each age, but I can't figure out a way to count ‘5 y/o’ without also counting ‘15 y/o’ — or a way to count all classes for ‘5 y/o’ including those that are also for ‘15 y/o’.

My downloaded data looks like this:

The results that I are want are:

If it matters, the number of classes varies by semester.

The following counts both classes for ‘5 y/o’ and classes for ‘15 y/o’ that are not also for ‘5 y/o’

=COUNTIFS('data sheet'!$A$2:$A,"<>",'data sheet'!$B$2:$B,"*"&A2&"*")

The following fails to count classes that are for both ‘5 y/o’ and ‘15 y/o’.

=COUNTIFS('data sheet'!$A$2:$A,"<>",'data sheet'!$B$2:$B,"*"&A2&"*",'data sheet'!$B$2:$B,"<>*"&A12&"*")

Thank you.

link to editable Google Sheet

Here's one approach you may adapt accordingly:

=arrayformula(countif(","&'data sheet'!B:B&",","*,"&B2:B22&",*"))