So as mentioned at the end of the last thread, I would update these calculated columns to be measures. Measures re-calculate every time they are displayed/used in whatever the current context is. Visuals apply context automatically for you in PowerBI. To make this easier with your data set, I would suggest you do create one calculated column on your table, that indicates the age range band a specific training took place. Call it [Age Band] or whatever naming convention you use.
How are you displaying the data? I'm assuming in a table or matrix visual, but this solution will work for other visuals as well. Can you show a picture of what you currently have and/or share a .pbix file with the sensitive data redacted? Even a picture of what a desired outcome would look like would be helpful. It will be much easier to determine how the measures should be set up with that information.
I've been trying to turn this into a set of measures, but how do you tell a measure to calculate how many people were in an age band at the time of an event, for every selected event and org? That's where I'm having my trouble.