In a couple of years, I am sure that with technology, they will be able to implant Arnold's brain into a Terminator cyborg body with artificial skin and then he will come back better than he ever was in the 70s.
I say let Arnold grow old however he wants. He doesn't have anything to prove to anyone. He did it all in his days as a bodybuilder in the 70s.
Arnold was smarter than most bodybuilders...he got out of bodybuilding and found something else to pursue (movies, politics, business, etc.). Otherwise, he'd be sitting at bodybuilding expos selling his photos at $25 per pop and trying to relive his past glories.