This is based on what I know without having an inside information or knowledge of the specific cycles/hours of the A330-300 fleet. Heavier checks, C and D, are usually occasions when airlines decide to retire aircraft other than returning leased aircraft. C checks happen every two years or so, give or take a few months, and are usually when major aircraft interior modifications take place, see AA's 777 CIP. D checks or Heavy Maintenance Visits, HMV, have to be planned several years in advance as so few shops perform them as it requires the aircraft to be taken virtually dismantled and put back together. HMVs happen roughly every six years give or take a few months. Aircraft usually undergo three or four HMVs before being retired.
As previously stated, AA's A330-300s have PW engines, the only PW engines in AA's widebody fleet. Obviously, this is a big reason why they are an odd ball in the fleet, not to mention their relative lack of range unlike say Delta's A330-300s they inherited from NW. (The 242 tonne A330-300 has the same range was the original A330-200. Incredible work by Airbus.) However, just judging by age and estimated cycles, AA's A330-300s are nearing a third HMV. Combined with their unique engine type, its about time these aircraft are put out to pasture.
AA will keep all A330-300s going into next year. Its possible AA will wait until the very last cycle for each aircraft before retiring them. (Something Delta has done regularly.) Also, the W retrofit is starting to get underway and won't be finished until the end of next June. (Personally I'd expect it will be complete next July and possibly even August.) AA will need as many widebodies taking place of those undergoing retrofit, especially since several will be modified during the summer. Lastly, the crews still have yet to be integrated. Supposedly it will happen next year. AA is already planning on using 767s on PHL-Europe flying. Expect the 772s mostly replacing the A330-300 routes ex-PHL in particular and likely CLT-LHR at a minimum.