9 months old. It was miserable and we didn't sleep well. We were constantly going in and picking him up every time he cried. It wasn't until we let him cry for a while- usually 15 minutes before going in and checking on him -without picking him up- that he finally started sleeping on his own very quickly. Halellujah!

The next 4 kids we started sleep training at about 2 months and every one of them were sleeping through the night no later than 3 months. It only takes a week or so if I remember right.

We checked on them every 15 minutes and soothed them without picking them up and holding them. It wasn't cruel. And it worked. Keep at it.