Diseases like cancer, dementia and Parkinson's are known to become more common with age.
The cause of these disorders is often unclear, with a combination of genetics and lifestyle habits often being to blame.
Writing in the journal PLOS Genetics, scientists from the University of Oxford have revealed genetics play less of a role in the onset of common conditions as we age.
Conversely, lifestyle habits – like smoking, a poor diet and being inactive – become of greater importance in our later years, the results suggest.
Better understanding why this occurs may one day enable medics to predict an individual's risk of a specific disease, allowing them to be diagnosed and treated earlier.
"Our work shows the way in which genetics affects your risk of getting a disease change throughout life," said lead author Professor Gil McVean.
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"For many diseases, genetic factors are most important in determining whether you will get a disease early in life, while – as you age – other factors come to dominate risk."
The genes we inherit from our parents influence our risk of a host of diseases, from cardiovascular complications to cancer.
Scientists can even assess a person's DNA to gauge their risk of developing a certain condition in later life. Nevertheless, an individual's age, sex and ethnicity can interact with their genetics to further influence their vulnerability to disease.
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To learn more, the Oxford scientists analysed the DNA of half a million participants of the UK Biobank study. The participants' genetics were then assessed relative to their risk of developing 24 common diseases.
Results reveal genetically-induced high blood pressure, skin cancer and an underactive thyroid usually strike in early life.
Over the years, too much salt, excessive sun exposure or previous thyroid treatment are more likely to be to blame.
Why our genes have less of an influence on our disease risk over time is unclear. The scientists expect an unknown process is at play, like an interaction between our DNA and the environment.
Better understanding this process may enable medics to more accurately predict whether an individual will eventually become unwell with a particular disorder.
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