what age?

Im thinking it depends. I tried it w my son and he just didnt get it. Hes a little over one.

I don't really use it most of the time when I tell her to stop she stops but I think around the age of 2 you can use it

Ds was 15 months old. Dd was around the same age I believe.

18 months.  They were just to get them used to the process early because they were too young to grasp the concept.  Because it's just always been that way, now that they are older I've never had to battle them to sit in timeout.  They do their time and we go on our way :)

WE neverf could do timeouts with Caden.  It just made things worse LOL.

My LO just turned 2 - two days ago - and we have been doing time outs for the last few weeks. We did one about 3 months ago but haven't had to do any for along time. Just in the last few weeks though we have had to do time outs ... oh probably 4-5 times a week.

we do time outs, have been since just before their second birthday. most of the time we try to avoid time outs though by going back and correcting the wrong. (ex. if its because they're hitting our cat, they go back and pet her gently) or something along those lines. 

It depends on the child in my opinion. We started at 12mo and it worked just fine to the point that we rarely enforce it these days (she is 31mo now). I often just threaten it or use the count to three method and she complies.

Right around 2 y/o

Depended on the situaiton and what worked and didnt work,.