Okay guys, after reading your posts, I'll clear this up for you. I fly for an American carrier, (Northwest) and I am American. Regarding the senior flight attendants that you refer to, you are generally correct in you observation that they are not the most pleasant. Some of the ladies began with NWA back in the 40's and 50's. Being that our airline has been in service over 70 years, you are bound to get some of this. Our number one on the seniority list turned 80 this month!
You are correct in your conjecture that seniority rules in our system. They can pick and choose their routes as they please. As for the union comments, this has nothing to do with when they choose to leave. Delta is a non-union carrier, and they have just as many elderly FA's as we do. The union does not entitle them to keep their jobs.
The international routes are generally the most senior because they are worth the most amount of hours in a single trip. Ergo, they try to fly schedules that allow them the most days off. You think the FA's that fly Europe are old, fly over to Tokyo. The minimum seniority level is about 30 years of service!