If you're going to fly somwhere where you either have to use your FAA ticket or are being issued a validation based on it, then the age limit of the country (in this case USA) that issued the basic licence applies.
This would be true if the FAA applicable part, specifically 14CFR61, set an age limit on the use of the FAA ATPL.
It does not.
The age limit applies to the specific 14CFR121, and that only.
If regulatory authorities elsewhere are applying this incorrectly, they need to be so informed by ICAO.
I have had no problem whatsoever in this regard, lately.