Hey what's up?
You're right about the retirement of the MD-80's. American is planning, in the long run, to phase out the MD-80's and replace them with NG737's. Over 100 737-800's have been placed on firm order, about 30 of those being delivered already, those are replacing the last 727-200's American still has (the 727-100 is, needless to say, ancient history). I think it's more likely that American converts some of the NG737's they currently have on option to firm orders, they will eventually do that to replace the 250 MD-80's American has. The MD-80's will likely be replaced with 737-600's and 700's, yes they are still young but as you pointed out, the oldest one is over 15 years old already, the first one entered service in 1984. I predict that the last MD-80 will be retired in 2015. By then, the 737-600/700/800 will be American's workhorse like the MD-80 is today. The 757's will be around at least 15 more years, if American ordered 20 more of those, that means that they plan to operate that type for many more years to come, those are young. The Fokker 100's are also young but those will also be replaced by the Boeings in the long run.
Tbe 767-200's are still young, but they will start showing their age in five years from now. I think that those will be around for 8 to 10 more years. The A300-600's will likely be replaced with more 767's (either more 300's or 400's). The DC-10 will soon be history and the MD-11 is also on its way out.
This is American's fleet plan in the long run:
2 narrowbody types: B737-600/700/800 and B757
2 widebody types: B767-300 and B777
American goes Boeing.