The Ending Of Old Explained

Throughout "Old" and its brisk 108 minute runtime, the viewer is repeatedly bombarded with new information and consternating wrinkles within the film's central conflict, but beneath all the intrigue lies the ticking time clock of the cast's survival. 

When the beach excursion begins, there are eleven characters with their toes in the sand. There's insurance actuary Guy (Bernal), his wife Prisca (Krieps) and their kids Maddox and Trent, each played by a trio of performers as they rapidly age over the course of the day. But they're joined by Rufus Sewell's doctor Charles, his wife Christal (Abbey Lee), his mother Agnes (Kathleen Chalfant) and their daughter Kara (also played by a trio of actors). Add to that, rapper Mid-Size Sedan (Aaron Pierre) who was on the beach when they arrived, and nurse Jarin (Ken Leung) alongside his wife Patricia (Nikki Amuka-Bird), a psychologist, and you've got a whodunit-sized cast of individuals of varied ages, each hurdling towards certain death from accelerated circumstances if they can't make it off the beach.

But one by one, as every potential exit proves untenable — trying to swim against the current kills Jarin, climbing the cliffside and falling fells an adult-aged Kara, everyone who tries to traverse the caverns surrounding the beach blacks out — the surviving inhabitants each succumb to the hardships of aging in their own respective ways, while accepting their fate and trying to enjoy the present with their remaining loved ones.

Guy and Prisca, on the verge of divorce when the film begins due to infidelity and a benign tumor causing the duo to doubt their future together, have no choice but to forget the troubles of the life they led before arriving in this peculiar nexus. Guy slowly loses his vision and Prisca, her hearing, but the two work together to fend off the violent threat of Charles — the doctor hiding a burgeoning schizophrenia that consumes him as the beach ages his mind by years in hours.

Nearly adult-aged Maddox and Trent (played by Thomasin McKenzie and Alex Wolff respectively) must hide from Christal, who has similarly lost her mind and is trying to murder them by heaving rocks from afar. The core family spends one final moonlit moment together, enjoying the peace and tranquility they initially sought this vacation for, even under suboptimal conditions (certain death looming on the horizon, for instance). Guy and Prisca die within moments of one another, mimicking a sped up version of how often elderly couples die within months of each other. 

When the sun rises the next morning, Maddox (now played by Embeth Davidtz) and Trent (Emun Elliott), who began this journey aged 11 and 6, find themselves in middle age, positive they will die but choosing to give escape one last chance. But not before building a sandcastle together, for old times' (yesterday's) sake. In the ensuing play date, Trent remembers the code-breaking game he played with Idlib (Kailen Jude), a child they met at the resort the day before. Idlib seemed to know more about this strange location than he was able to let on, but when Trent decodes the final letter he got before they came to the beach, it reveals a portentous message about the potentially protective powers of the nearby coral.

This convinces Maddox and Trent that swimming through the coral may protect them long enough to get away from the beach and whatever mysterious energies have been hounding them.

But when they try to make this underwater trek, Maddox gets her swimsuit caught and the two appear to drown, the final members of this trip extinguished for good.