No, but you can create a similar effect
Reduction in Lifespan
As cowlinator said, there aren't any natural phenomena that kill every person in a certain age group. You could argue that certain diseases might be able to do so, but it would be unreliable. However, we can vastly reduce the average lifespan of your colonists so that living past twenty-five is incredibly unlikely.
Cause of Death
There are several directions you could take in reducing the average lifespan of a human, but one which I feel holds a lot of potentials is forcing every colonist to develop pulmonary fibrosis. This is not only consistently fatal unlike disease or natural disasters, but is currently incurable and probably still would be for your hypothetical colonists.
If the atmosphere of the planet was sufficiently saturated with a fibrous particulate, the development of progressively worse pulmonary fibrosis would be inevitable. You wouldn't be able to avoid exposure even with future-tech filters.  There are probably ways to industrially cleanse the air, but it's unlikely your colonists would have the necessary resources to do so.
The easiest explanation for the presence of these particles would be the byproduct of a biological process. More specifically, the byproduct of aeroplankton. Without delving too deep into speculative biology, you could say an event similar to the Great Oxidation Event occurred after this specific aeroplankton was rendered hyper-viable by the tampering your colonists did to the biosphere.
I tried to find an example organic particulate to model yours after, but there weren't any low hanging fruit. So, just think things like silica, asbestos, and smoke.