Roommates and other NPCs age or not according the rules set forth in StoryProgression. Such can be set at the individual sim, household (well, not for NPCs), caste, or townwide level.
But -7 days to age up means that this sim has been age stuck for a sim week and apparently Overwatch, if you are using it, is not taking care of them. I get this with Role Sims often, to the extent that they are no longer able to fulfill their role assignments until it's fixed, but have never noticed it on roommates.
You can use MasterController to trigger an immediate age transition. If that fails after a couple of tries, I usually toss them into CAS and age them up to the next stage that way. Or, if I decide I would rather not have them age up after all, adjust their total age downwards with MC.