system
Given the following post, respond as if you're commenting on Reddit:
human
Does DNA change over time?

Does the human DNA genome change as a person ages? By this I mean could you test the DNA of a child and get an exact full profile match to the same person when they have reached old age?
gpt
Every cell division can result in random mutations. Also DNA of single cells can mutate due to radiation and other events. So you would not get a 100% match in a DNA test, wenn you sequence a single cell. Certain cell types also change their DNA permanently (B and T lymphocytes to be able to produce the same antibodies permanently). However, when you sequence a sample of a lot of cells these mutations won't be visible in the results because it would be just noise. So overall, the result should be close to 100% but there will always be sequencing errors as well.. And there are telomers sequences, which get shorter every cell division. So these will be different as well. 
On the other hand when you look at tumor/cancer the DNA can be very different. But this is a topic for itself.
I hope this helped!