I have encountered age stuck sims, the ones I am actively playing but more commonly inactives and NPCs, many dozens of times. I have always been able to fix them with some combination of MasterController and DebugEnabler commands or just letting Overwatch do its thing. At the very least (not the best solution) I bring them into MC's version of CAS and bump their age up myself, if it's possible to get them in. The resulting sim may glitch and produce some errors for a bit, but they usually sort themselves out.
Sometimes the old fashioned trick of evicting the household in Edit Town, making a copy of their residential lot, bulldozing the original, placing a copy, and moving everyone back in also helps.