If you want to grow from seed (or seedling) your best bet is to grow it in the ground for a few years to thicken the trunk and periodically prune/chop to produce taper and movement. As far as development and styling are concerned, my teacher (Ryan Neil) approaches it cyclically. You allow the tree to get super vigorous, so it will tolerate a severe styling. The tree is then allowed to regain vigor, which leads to its outgrowing its design. With each subsequent styling, some of what was is removed, leaving behind deadwood and/or negative space to advance the visual age of the tree. So, with each trip around the cycle, the tree attains a more ancient image. It’s important for you to understand that you don’t grow an aged bonsai from a seedling. That would take hundreds of years. You create an image of age by applying bonsai techniques. Also, to keep a tree healthy in the long term, it needs to be allowed to grow between stylings.