You can't undo it when you save.
Chat with our AI personalities
You can't undo what you already bulldozed.
you can't
The Sims 3 have 4 save slots.
i dont know about ''undoing a birthday'' but i do no how to stop your sims from aging ( getting older.) if you go on the ''...'' sign, when you click to save the game, go on options->game options and it says ''enable aging'' un-tick that box, then you wont get old
Sorry to say but you just got to lose all the unsaved data. So for future remember to save a lot!