The Devaro Twins
Jason and Jaina are twins, but it's really just in the face.
Oh, when they were little, they liked to copy each others outfits and trick anyone they could into confusing them. But as they grew up--grew into themselves-- it became easier to tell them apart.
Jaina liked her hair long, long enough she had to keep trimming the ends because of them always getting caught in a drawer or the ties on some of her outfits. And she hated doing her hair up in braids or buns or even a ponytail--though she did tie it back from time to time. Eventually, she cut it. Now it's only to her shoulder blades, long but not enough to catch in anything. It surprised her brother and grandfather when she came back from a mission with a Trader caravan--smaller than when they'd left, with injuries mostly healed--with her hair less than half as long as when she'd left. No one commented on the dusting of grey at her temples as she grew a little older.
Jason liked to copy photos of old military cuts, but preferred enough on top he could comb it over. He hated shaving, but hated his slow to grow in 'beard' more, so he never had more than a five o'clock shadow. But he, too, came back from a Trader mission changed. Short beard, well, more of a goatee unless he couldn't find the energy to trim the rest. As he got older, his hair too started to dust with grey.
He and his sister were barely starting their 30s, and despite their grandfather saying he and their parents had started to gain a little grey in their early 20s, they thought of the added color more as a sign of their lives than their genes.
Now they rarely took missions separately, despite love dipping into and out of their individual lives. They didn't want to come home and find the other suddenly changed. It may not have been much--one event each, that subtly changed them--but once was enough to make them decide to never go without the other into the dangers outside wherever they called home.