DD11 almost did this on our last trip, but decided to ride Soarin' again instead!!!!
If you are facing the various food stations, the cookie baking area is to the far left of the lower level. It's directly behind the area where you would wait if the line for "Living With the Land" was long. I think it lasted about 45 minutes or an hour, long enough to make and bake some cookies. I don't remember the posted age limit, but it wouldn't be appropriate for someone who couldn't do the same activity with limited supervision at home (ie no toddlers or smaller preschoolers.) There's a posted schedule, but I don't remember what the times were. You line up to secure a spot for the next time, so I think you stand in line about 15 or 30 minutes watching the previous class before it's your turn.
We did go and buy chocolate chip cookies and we had a milk and cookie break!!!