When Do You Decide To Age Your Sims to the Elder Lifestage?

I age sims up when I feel like it. I play exclusively with aging off, but I have turned it on once or twice very briefly. I've never been big on family gameplay up to this point. I have one save right now where families will eventually become part of the story but I still plan to control when the kids age up. I am looking forward to the infant update and the new pack even if it ends up only being used for that one save.