We know that Guts was gone for a year after leaving the Band of the Hawk. We also know that after Guts and Casca conceive a child that was corrupted during the eclipse by Griffith, and that this conception occurred AFTER Guts returned. Additionally, it’s suggested that Casca suspected she was pregnant at the time of the eclipse. So conservatively, that’s 13 months or so following Gut’s departure from the band of the Hawk. But a lot happens in between just first appearance and Guts departure from Band of the Hawk.
There are 2 more major battles in the 100 Year War, and a few significant events for the main characters that happen in between. And by ‘’major battles” I mean battles between the midland army and the opposing army. The 100-man-fight and similar minor skirmishes don’t count
Those skirmishes could have happened anywhere and anytime, but it would have taken middle-age armies some time in between each battle not to mention the weeks or month that it would have taken an average middle-age army to mobilize to a war-zone in the first place. Then they would have needed time to set up camp and such before attempting battle— anyway you cut the major battles (and the surrounding minor events) suggest there was at least 9 months in between his first appearance and Gut’s departure.
So by my very rough estimates that’s 18 months. The kind of aging that we see here just doesn’t make sense. After all, it’s not just his hairline. His skin is hanging more and has more wrinkles. Hell, he can barely stand on his own after the time has passed— people just don’t age that fast, and in a series that displays aging in a parallel Way to the way it happens in real life, this stands out.
It makes me wonder if there was something supernatural that made him age that way. I wonder if maybe the God hand made him deteriorate faster as some form of punishment for the way he treated Griffith. Even though his torture ultimately pushed Griffith into joining the god hand, which is what they wanted, the king still had one of the guard hand brutally tortured. And I don’t think they would forgive that.