I think alot of it has to do where they are behaviourly. We put Matilda into a bed at 16 months because she started climbing out of the cot & then climbing back in. It got so she was avoiding sleep just to jump in & out.

So we started in the big girl bed. It took us months to get her settled in a sleep routine too. But we continued to use our nighttime routine and just sat at the end of her bed until she was asleep at first.