The findings were published in the journal Aging-US by researchers David Gems, Alexander Carver and Yuan Zhao.
According to the scientists, the first stage begins earlier in life when the body experiences damage from infections, injuries or genetic changes.
Although the body repairs much of this damage, some hidden problems may remain for years without causing illness.
The second stage happens as people grow older and the body gradually becomes weaker. Researchers say this makes it harder for the body to control earlier damage, allowing diseases to slowly develop.
The scientists believe this may explain why some illnesses appear mainly in old age even though their causes may have started decades earlier.
For example, viruses that stay inactive in the body for years can become active again when the immune system weakens, leading to diseases such as shingles. Injuries suffered during youth may also later contribute to arthritis as body tissues age and lose strength.
The review also suggests that some inherited genetic mutations may remain harmless for many years before increasing the risk of diseases like cancer later in life.
Researchers say the new model could help doctors and scientists find better ways to prevent chronic diseases by reducing damage earlier in life and improving health during aging.
The study presents aging as a complex process caused by many factors working together over time.
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