Captain on first trip after age 60 does not take into account ages of First Officers when planning crew rotations on four leg international trip. Result; two pilots over age 60 at controls during landing at foreign destination.

Narrative

This was my first trip after birthday number 60. The age 60 requirement is that below 10;000 FT at least one pilot must be younger than 60. I didn't think about this requirement - which now applies to me - until after the second takeoff of a four leg trip with a First Officer who is himself over 60 (first and second leg rotations were based on normal considerations for takeoff/landing currency and break preferences. I was in the left seat for the first leg takeoff but due to Captain augmentation; not in a pilot seat for the first leg landing. I was in the left seat; with the 'over-60' First Officer for the second leg takeoff but the 'under-60' First Officer was with me in the seat for the second leg landing). During the second leg our 'under-60' First Officer who was not with us on the first leg - thought about our ages and realized that we had not correctly provisioned our crew rotation. The second leg's approach phase and all subsequent legs had a correct rotation with at least one pilot younger than 60 in a seat below 10;000 FT. I'm embarrassed that I didn't think about this matter as I certainly knew of the requirement but since it hadn't applied to me until recently I just didn't think of it. In discussing the situation with the 'over-60' First Officer I had the feeling he hadn't previously run into this situation either. No excuse. I will now pay close attention to the age 60 information provided in the crew list!