Ronald Held wrote:
I can see Cromwell's Cochrane behaving differently seeing as he somehow survived WW III and his team continued to work on the warp drive program. Maybe he is suffering from deprivation and radiation . poisoning?
You expect the rejuvenated Cochrane to look much younger but how much mental changes came from his long period of time interfacing with the Companion?
The movie's novelization by J.M. Dillard postulated something to that effect (that Cochrane in 2063 was suffering from radiation poisoning to a certain extent), and that it was the Companion who later rejuvenated him, at least physically.
Although, yeah...can't really account for the mental differences beyond a similar sort of intervention. The novelization does make mention that Zefram had been subject to psychological issues prior to WWIII, and had received an subdermal "upper" drug-implant (the late-21st century equivalent of Prozac, essentially), but that it had long ago depleted its dosage after the nuclear war took place and destroyed all the pharmaceutical companies.