It is found that human genomes tend to alter their characteristics with change in environmental or nutritional factors along with age. It occurs due to the epigenetic changes over the course of life. These changes are influenced by the environmental exposure and dietary. These epigenetic are also thought to influence the changes related to the health of a person with age, like development of diabetes, autism and cancer. The main epigenetic modification noted in the DNA sequence is in the methylation. On research it is found that abnormal levels of methylation can lead to diseases, like higher levels might even turn off genes and low levels turn on. Thus, epigenetic of a person does changes with age

any advice on how to reduce this methylation?

I guess that sounds reasonable enough. Everything alters with age. It's a big part of being human, and it's an even bigger part of life. You can try to slow down the change, but it's pretty much inevitable.

I guess prevention seems to be the only option. Scientists have tried to change genome structures which are often accompanied with wide side effects (mutation).
Environmental factors are major cause which is difficult to control.

There is still a huge between our current knowledge on DNA and what it actually really is. This may sound strange to some but it is possible to prevent diseases and even regenerate our bodies with the thoughts. Don't misunderstand me as I am not talking about some magical process here. Those who have been studying mind powers will definitely resonate with it.