Hi Timofey, the correct sentence is 'When I grow up, I will be a doctor'. Note that we always say 'A doctor'. This is a form of first conditional - describing a possible/ likely future event. I hope that helps!

A child can say: "When I grow up, I want to be a doctor." An adult can say: "I grew up, and became a doctor."

"When I grow up, I will..." is most common, we often ask kids 'what do you want to be when you grow up?' and this is how they answer. "When I'm grown up, I will..." sounds a bit more childish but it's fine "When I have grown up, I will [have]..." is odd to me. I think it's a different tense structure. e.g. "When I've studied languages before, I've used italki" is fine -it implies something you've done multiple times. Sidenote: there's a great song called 'When I grow up' from the musical Matilda - it's on youtube if you want to watch it!