Yeah I have aging off so I assumed I wouldn't get any birthday invites until I switched it back on. But nope, got one the other day from a friend who is the same age as my oldest Sims, as I make it a point for my Sims and all their friends to be around the same age. I also have aging set on the longest setting, so basically no one should be aging up anytime soon, whether aging is on or not everyone is around 50+ days before they reach the proper adult age. But since I read that getting invited will age up the Sim inviting you I decided to decline.
