That is my companies understanding as well. On international trips Captain must be under 60, FO dosen't matter. It is a recomendation by ICAO that many countries enforce. It is just easier not to have to worry about what country enforces it and what country dosen't. After Avjet was fined in Europe for having a Captain over age 60 most Southern California 135 on demand companies have moved in that direction. I realize that the rule is more complex then I am making it out to be be but my company has tried to simplify it, as many other companies have as well.