I'm old as well and was lost as to how to correctly set this up. I'm not even sure if this is the correct way but it works for me.
1st. Define in the stashing section were the recipe items are held.
2nd. In the recipe section blacklist all other tabs, otherwise it might take those items into account.
3rd. Enable the gear recipe within the recipe section.
Now once it has a set of items that qualifies for the vendor recipe it will them take them out and sell them for the chaos orbs.
Also, I used the high end rules available in the forum and tweaked it to my taste.
Hope this helps you guys.
As for how to properly use he following rule, I have no clue but if anyone of you figure out please share as I would like to know as well.
Also go and clean out the tab for the recipe items, all of the items are required to be iLevel of 60 or more. to find an item iLevel just hit alt and mouse over the item.