We started the “time-out” thing w/our 1st DD at around 16/17 months. We use the corner. I was a little scared I started too young but actually b/c we started young, her response to it has been fantastic. She’s 26 mo. now and when she’s misbehaving, we tell her to go to the corner, of course she starts crying, we make her go anyway and we tell her to stay there until she stops. We then let her come out and if she starts crying again, we simply put her back in the corner. There are times, we’ve had to spank her, then put her in the corner but it’s what has worked for us.
It’s actually funny b/c now w/our 6 mo. old, my DH seems to have forgotten what an infant is as he tends to be stern w/her when she starts crying a lot. I’ve actually had to remind him that’s her only way of telling us she’s hungry, etc. If any child will be scarred from starting discipline too soon, it may be our 6 mo. old!
Michelle is right about relatives’ criticism… even my sister tried to stop me from disciplining our DD at McDonalds. Needless to say, I had to stop my sister from trying to give my DD a toy to quiet her until we got outside! (Yes, it did irritate me!) However, I promise, the sooner and more consistent, the better the outcome!