I soak freshly processed turkeys in a bucket of salt water for approximately 8 hours and then let them rest in the refrigerator for 3 days before cooking. I haven't had any tough turkeys.
There has been plenty of information on this subject posted in the Meat Birds ETC forum.
The first question that comes to mind is Did you let the processed bird "rest" before cooking?
Turkeys at those ages should have been very tender but if you don't allow the processed bird to "rest" in the...