My kids all trained at diff ages. My first 2 (boy and girl 1 year apart) trained together. My daughter took off, but then when she saw her older brother taking longer, she started copying him and held back. All in all, they were almost 4 before they were totally trained.
My 3rd child asked for a potty chair one day when he was 2yo. I brought it home and he jumped up, stripped and then sat on it beaming. Stood up and proceeded to pee all over the floor. LOL We told him that's what he needed to do in the potty next time. So he did. He was trained - both wet and poopy diapers AND nighttime in 3 days. He was my miracle potty child!
My 4th wouldn't go near the potty. When he was 4yo he had his eye on a toy. So we bought it and put it on the fridge where he could see it, but not open it.
Then I put a chart in the bathroom & every time he used the potty he got to put a sticker on the chart. After so many, he earned his toy. AND - he was potty trained except for the occasional accident.
Now, I'm on my last kiddo...still working on him.
Bought a story about potty training and I changed the names in it to him and his brothers. Also bought a video of kids using the potty. We'll see....