One's chronological age is how long one has been alive, while one's biological age is the age of your cells and systems based on physiological information. The two ages may be the same or they may also differ, sometimes significantly. Your biological age is effected by your genetics and by environmental factors such as stress, exercise, diet, sleep, and other factors. Biological age is a better predictor of possible disease and death than chronological age.
Biological age determination is now readily available, so I decided to give it a try when I first read about it almost four year ago. Here are some good introductory articles on biological testing, focused on Elysium Health's process:
Elysium Health's Index ($299): (link)
When you place an order online they send you a kit that you can use to return a saliva sample. Elysium then extracts your DNA and analyzes DNA methylation across your genome to calculate your overall biological age. They now also determine the biological age of various systems in the body (brain, liver, metabolic, immune, hormone, kidney, heart, inflammation, and blood), and also provide science-based lifestyle recommendations.
I first did Elysium's Index Jan 2020, followed by repeating testing in July 2022 and September 2023. As you can see the results were internally consistent over the years, with my biological age running at approximately 90% of my chronological age. Initially Elysium only provided the overall biological age; however, they subsequently refined their process and began to also provide the biological age at a system level. Previously I had felt pretty satisfied with my results since I appeared "younger" than my chronological age; however, when I received the additional detail I was taken aback that the picture wasn't that positive, especially the 'brain' result!
My state of mind wasn't helped by running across this article, 'Higher Biological Age May increase Stroke and Dementia Risk' which found: