Responses
True but the manga talked about a lady that wanted to stop being immortal after seeing all her lived ones die. In her case she was an old lady that became young after eating the mermaids flesh.
I thought that he stayed old since his mermaid didn't care about what form he was in. He just wants him old or young. Also he did ask him to finish the horn and he has hardly eaten any of it so maybe he would turn young if he did finish it.
Maybe he didn’t gain youth since he didn’t eat him.
I think Kiyo was immortalized by Chiyo when he was ALREADY an old man! That's why it looks weird that we don't see Kiyo as a young man. Even in their flashback 59 years prior, he already looks old.
So yeah, being turned immortal doesn't mean Kiyo turns young again. His age was just "stopped".