Since 'no State can force another State to accept its own deviation from an ICAO Standard', from 23 November 2006 the US will not be able to prevent a foreign carrier from operating in its airspace with a PIC aged up to 64. The following is the relevant extract from the ICAO website:
A State may wish to impose a lower maximum age limit than that specified by ICAO in 2.1.10.1. It may do this for the licenses it issues, but, as stated above, it cannot prevent an aircraft operated by a PIC holding a licence from another State, who is below the ICAO upper limit, from operating in its airspace.
Regards,
Mel