How do you make your neighbor grow up?

you can do a cheat by pressing ctrl+shift+c then typing boolProp testingCheatsEnabled true then hold the shift button and click on a sim and chose 'spawn' then you will spawn the tombstone of l&D and then you can click 'add neighbor to family....' and then
add the neighbor you want. then, shift-click the neighbor and click age transition. and you're done! :D