I waited until my son was two. We expected it to take a few months but we concieved literally five days after his birthday since that's the month we started trying. 😂 We'd planned on him probably being just over three or so when the baby was born but she was born four months before he turned three. It's a good thing though, he absolutely adores her and hes old enough to "help" me with his baby sister by handing me diapers and stuff and talking to her to entertain her. He's also independent enough that he can entertain himself with his toys for a little while when I'm tending to his sister. I think we got really lucky with him being the age he was when we had our second.