Originally 1950’s vintage.
All now completely rebuilt with "Glass Cockpits", and more powerful engines. Service life extended maybe another 25-30 years. When better birds are built, Boeing will build them. If it ain't Boeing, I ain't going!
No, actually it was a separate development. The 707 and the KC135 are both derived from the 367-80 prototype. The KC135 is narrower, shorter, more heavily braced, and actually preceded the 707 airliner. The famous Tex Johnson barrel-roll was done in the -80. You can see it on display at the Udvar-Hazy Center near IAD, next time you're in Virginia.