There is nothing to engage with. I think tersely. Some researchers could learn.

I find it annoying that a large part of research is the obsession of taking a perfectly smooth, gradual phenomenon and introducing artificial boundaries, sometimes even with formal labels. And then we spend the next few decades rolling it back as we inevitably find out that reality is nuanced, and the arbitrary categorization is more of a distraction than a meaningful tool. But I'm sure this fantastical finding was great for somebody's career.

Meaningful categorization is a necessary and foundational aspect of science and understanding in general. We categorize matter into categories such a solid, liquid, and gas, because this has meaningful consequences beyond merely temperature.

If you think the categories in this article are useless, you're going to need to justify that. Aging is well-known to encompass phases with nonlinear transformations, such as puberty or menopause.

So what you find "annoying" is actually a building block of science. And while disagreeing in a particular case is certainly valid, you're going to have to either present evidence to the contrary, or else find weaknesses in the particular methodology used.

So there's plenty to engage with. But you're not doing it, so your comments are just snark with no value.