707 production ended in the early 90s with the manufacture of USN E-6As and the joint RAF/French E-3D/F buy; the very last 707 off the production line was ZH107 which was delivered in 1992. The NATO E-3As were all delivered between 1982 and 1988 but have undergone several modernisations in the interim.Boeing 707 - last airframes built in 1978 IIRC
Inefficient engines. They are starting to make Shacks look youthful.
All commercial 707s are now retired.
As stated, there is a large spares pool available to keep even P&W powered jets going for some years yet. As the KC-46 replaces the KC-135 in USAF service, that pool will rapidly expand and the USAF have no plans to shift their RIVET JOINT/COBRA BALL/COMBAT SCENT/CONSTANT PHOENIX onto another type any time soon.