Not sure what type of pie charts you were interested in creating, but one quick way would be to just change the mark type to Pie, then move Measure Values from rows over to the Angle card:
It also might make performing more analysis on the data easier if you pivoted the age range columns when initially connecting to the data source:
This will leave you two columns, a dimension that has members equal to the names of the columns you pivoted, and a measure that has their corresponding value.
If the pivot functionality does not end up working we'll probably need a little bit more detail on the exact type of format you'd like for the resulting histogram in order to come up with a solution.
Hope that helps, thanks!
Dan - thank you so very much! Both of these helped a lot.
After pivoting the data it was a breeze to do the pie charts, tree maps and bubbles that I wanted to offer as options for my editor.
I also figured out how to do a regular old bar chart (not a histogram) that put the age groupings as I wanted them.
Very grateful to you.