Is there an upper age limit for pilots freight only?
The only situation in which a US-licensed pilot is subject to an age limit is part 121 scheduled airline service. Other than that there are no age limits, you just have to be able to pass your medical exam.

However, you state that in your scenario the pilot will have to be able to fly cargo in and out of the US. That implies the pilot may have a foreign license, in which case you must refer to that country's regulations.