DS was 3-4yrs old. His grandparents trained him.
DD1 i started about 2-3yrs old with getting a little potty and panties, getting potty DVDs, etc and she was NOT ready. She just wasnt getting it. Finally about 3, she magically got it. It was quite random. One day she woke up and said " I need to use the potty" and we went from there. she had accidents at first, but was better. She sadly at 5 still wets the bed. Its genetic though.
DD2 i waited until that magic moment like DD1, it came about 3 and the same way. One random day. She is dry all night and day at 4.
Theres no magic age, no magic way. It really is a random thing you CANT push them to do.