I've done it since my daughter was born she's now almost 6 months and she's fine I make sure to keep it beneath her shoulders once I fall asleep for the night
they say a year. I honestly put a blanket on my 7 week old. I make sure to keep it away from his face if he actually sleeps on his back. He normally sleeps on his belly. I do a lot of the no nos but I do what makes my baby comfy.