Most experts recommend starting when your baby is between 4 and 6 months old. By about 4 months, babies have typically started to develop a regular sleep-wake cycle and dropped most of their night feedings. These are signs they may be ready to start sleep training. Many babies this age are also developmentally able to sleep for long stretches at night.
"I have a 6-month-old who has refused to sleep longer than 30 to 90 minutes day or night since he was born! I've tried everything out there except CIO. He's strictly breastfed and relies on that or rocking to get to sleep. He doesn't know how to soothe himself to sleep, and he naps for only 15 minutes. I'm severely sleep deprived. I don't have the heart for CIO, but I think I'll try the revised method where you pat him down and reassure him lovingly while allowing him the opportunity to comfort himself. He's been co-sleeping since day one, and it's going to be tough, but I'm at my wits' end and cannot function."
There’s also no need to institute a regimented cry-it-out plan if what you’re currently doing is working for your family. But good sleep habits never hurt, and being able to fall asleep on one’s own is a necessary life skill. If you sleep-train at a time that’s developmentally appropriate for your baby and with the basic ingredients of healthy sleep in place, you can minimize the amount of crying your baby (and, let’s face it, you) will do.