I think you should learn calligraphy when you first enter elementary school.
Because this is the time when you have just entered elementary school, it is the beginning of learning habits, and writing well is a long-term habit and a habit that needs to be developed from an early age. At this time, you are not too busy studying and have the energy to practice specifically. Learning to write for beginners will be of great help to the learning of Chinese characters. At this time, learning calligraphy can be less intensive to cultivate children's interest. After all, interest is the best teacher.
Children under this age who learn calligraphy are not literate at first. Their bodies are still very immature and their physical strength is relatively weak, so it is difficult to concentrate, because the study of calligraphy is a study that tests the perseverance of the body and mind. Therefore, this time is not suitable for learning calligraphy. It should be used to cultivate other abilities and give children a free childhood.
If you are older, if you have not developed good writing habits before, you will be troubled by some shortcomings in learning, and it will be relatively difficult to change. Moreover, today's children have a lot of academic work and cannot concentrate on getting started. The learning of calligraphy requires long-term persistence and hard work. Start at a young age and gradually learn in depth. This will not only make your children good at writing, but will also help to train your children's perseverance.