Does anyone know if there's a cheat and/or mod that allows us to age up non-played Sims?

I recommend the heirloom cake from simlogical. It is a birthday cake you buy in buy mode and light. Then you can bring someone to the cake or tell your sim to blow out the candles. If the sim is an elder, they will die of old age. It's one of the few things I had that I got from a site other than MTS, but it was recommended on that site.
simlogical.com/sl/Sims2Pages/Sims2_Aging.htm