"Can't anyone die of old age in Trek?"
I understand that sentiment. I had no issue with how Scotty went out (if he went out . . .). Granted, it is comforting to think our heros died peacefully surrounded by loved ones and surely some will/did. But many who refuse to retire don't go down entirely peacefully. Most of our past explorers during the heroic age of exploration died on the job: Magellon, Cook, Scott, Shackleton. Though I wouldn't kill everyone off during an eventful story, it is likely many explorers into the unknown will not die at home in bed, even in the future.