A way to use birthday cakes with aging off?

Birthday cakes for actively controlled sims are supposed to still be usable when aging is switched off. In fact, a mistake players often make is to switch the game's aging control back on when a sim is on the last day of their current age stage and then also present them with a cake. If done in relatively rapid succession, the sim stands to age up twice -- once for just being old enough to do so and once for the cake.

Possibly the sim(s) in question are not responding to the cakes because something else is wrong, such as an issue with their current outfits that do not allow them to yield to an age-up properly.