Some chapter 13 teaser pics show a new "young Hunter" character, and there is a theory that "old Hunter" may have cloned himself and swapped his brain into a younger body. That's not exactly plausible based on current medical science in the real world, but Power Vacuum plays loose with science and so it might be possible within the story.
I mean we know for a fact that it's Hunter. We know cloning exists because of Anabelle II, young Hunter has surgical scars along his neck and head, and after the first teaser with YH WWG commented to confirm it was Hunter to remove any confusion.
Also a brain transplant is actually plausible in real life. Especially for someone with the ethics and wealth of Hunter.
Somewhat successful head transplants have been done with monkeys and dogs since the 70s. They were alive and could look around, hear, and eat, although they were paralyzed due to us not having the ability to connect the spinal cord and it's millions of nerve fibers. The immune system of the body attacking the foreign organs of the brain is also an issue.
These problems are however reduced by cloning which has also been accomplished IRL with animals. An identical clone would remove the issue of the immune system and reconnecting the nerves would be far easier as they already line up and are compatible. Gene editing, stem cells or micro surgery would be need for the nerve repair.
The procedure would be extremely expensive which is why Hunter is whoring families out all over the world including his own.