Our sunflower is over 3 metres tall now, and still no flower. It was grown from a seed and planted straight into the ground once it had reached about 20 cm. What have we done wrong?
It could be that the seed you grew it from was a hybrid. All plants grown from seed show seedling variation, but plants grown from hybrid seed can revert to the characteristics of the parent plant used to develop the hybrid. It might be that height was a characteristic bred into this sunflower variety and you are getting that showing in this seedling. It might not flower or only have a small flower.
Oh, my word, that's tall, but what a shame, no flower! We have several in the garden. None so tall, but all with flowers! Looks like you'll eventually get a flower though.
Interesting photo!