For me, if you want to look old, a short hair do will do it, usually long means youth.
But they're probably thinking it like when your born you have no hair but as you grow it grows, so they're sticking to that. Kob looks pretty no matter what. Even as the dirty and hunch back E-Yen in "Nang Tard" she had virtual no make up and was still pretty (in a natural way), not plastered with make up or fake eyelash.