Timing of breast reduction after having a baby depends on several things. First of all, you want to be at your ideal weight so that there would not be any changes in breast size after the operation. The exact timing will vary because women lose their pregnancy weight at a different rate. Next thing is breast feeding. If you are breast-feeding your baby, you have to wait until you are done with it. You want to make sure that the breasts have settled to a stable size without active milk production. Therefore, if you have not breast-fed and have lost your weight successfully, 6 months should be adequate. Otherwise, you should wait until milk is dry and weight is down. Lastly, you need to consider your family plan. If you are planning on having more children, you should wait until you are done with child-bearing.
Flying after an operation is no problem physically. The concern is mainly possible interruption of follow-up care. You want to make sure there are no complications and healing is progressing well before you travel away from your doctor. This may take a couple of weeks. However, it is not a hard and fast rule. If you have a good doctor available where you are traveling to, it could be sooner.