Reading this article reminded me of the Komogorov axioms[1], which are basically a way to define probability "by the envelope", that is, without dealing with th

Reading this article reminded me of the Komogorov axioms[1], which are basically a way to define probability "by the envelope", that is, without dealing with the serious and complicated essence of it. Mitteldorf and the authors he criticizes, Colchero et. al., all seem to be trying to go the same way with aging. So I wonder, how can age and aging be defined mathematically, the messy way? If age were related to entropy, one could think of age as some sort of function on entropy. But despite all the hand-waving, I haven't found any evidence of biological age being related to physical or information entropy. Rather, I think people like to connect them to show that aging is inevitable and irreversible. Which, by the way, Colchero et. al. seem to be doing too by looking at some pitifully small amount of data. It is not[2]. IMO, the purported connection is more of a political, moral or religious statement than a scientific one. Here is a simple definition of biological age I like to use: an organism which is not at its prime, is old. Basically, one picks an _arbitrary state_ in the lifetime of the organism, the "prime" state, and builds the notion of age as how far in state space the organism is from it. By this definition, a newborn human is (by my fuzzy idea of prime state) 21 years old at birth, and then during the next 21 years, for each birthday, their biological age decreases by one. At what we call the age of 21 years old, the "prime" state, the person is 0 years old by this definition, and from there on, the age goes up. If describing the biological state of a human being seems overwhelming (it most certainly is), one could start with something simpler, say a bacterium, or even a totally made-up organism living in a computer, and try to model all the ways state can fluctuate. If one does that, I bet we will find the following: - It is possible to design/find an organism state which is a stable attractor[3], and it is possible to make that state arbitrary close to "prime", or close enough to be considered "eternal youth". I'm pretty sure that from the point of view of natural selection and population dynamics, such a state attractor would be a death end more often than not. But for the question of human immortality or eternal youth, it could be a really nice start. In particular, it will change the question from "is aging a physical/biological inevitability?" to the more constructive "how does one create unaging organisms?". This last question has more of a heretic charm than the (insert-your-adjective-here) take from Colchero et. al. [1]: https://en.wikipedia.org/wiki/Probability_axioms https://en.wikipedia.org/wiki/Probability_axioms [2]: https://en.wikipedia.org/wiki/Turritopsis_dohrnii https://en.wikipedia.org/wiki/Turritopsis_dohrnii [3]: https://en.wikipedia.org/wiki/Attractor https://en.wikipedia.org/wiki/Attractor