That movie is a straight up metaphor for neurotic behavior, the inability to accept adulthood.
the movie depicts a man who has rejected the Pain of Life and like most people, is therefore living the same day over and over
he lives in a perpetual gloomy winter
he is poisoned with self-loathing and this has made him cynical and unpleasant. he keeps trying to ease his emotional pain with alcohol and other empty creature comforts
he keeps rejecting the inevitability of pain and death, as symbolized by trying to keep the old man alive
finally, he gives up and accepts his own mortality, he drops his obsession with childhood
this lets him drop his defenses, he no longer feels the need to push people away, and he can finally enjoy the world around him, become a caring and worthwhile person.
at the end, he is released from his "prison" and decides to make puxatawney his home.
note that at the very end of the movie, he says, "we'll rent to start". that's him cleverly and slyly asserting his old personality. that's the real dead giveaway as to the metaphorical nature of the movie