Young Ian's shaved head and other Mohawk things

Sorry if this has been asked before, or talked about. I'm new here, and can't find a way to check previous topics.

But Ian's shaved head with the crest of hair on top with braids is something he actively needs to keep up. If this was real life, that lengthy journey across the ocean with Jamie and Claire would have meant he should have had growth showing after such a trip. Even after the best of times during his adventures, he should show some stubble after a day or so. But he's choosing to look this way. Meticulously.

I get that the actor has shaved his head, and has a dead rat attached to his head, but why is Ian, the character keeping up this Mohawk style when he's clearly not Mohawk, and has spent more of his life as a Scot than a Mohawk to devote to such a change, now that he's with his family again? How long was he actually with them? I can see the leathers and proficiency with the bow, but is there something I'm missing? To the book-readers, is there a reason for his attachment to remain this way while immersed now with his family and old culture?

EDIT: Thanks for all of the replies and explanations, especially coming from the book. The show really does seem like time is condensed. (Ironic for a time-traveling theme.) But after reading that there was more to it from the book, and he lived there longer than is suggested, and in the book, plucked rather than shaved, and had made a personal and spiritual connection to remain Mohawk due to the age he first lived with them, I understand now. Thanks, everyone! And thank you mods, for allowing me to post this question.