But starting Jedi training young has important narrative function. They do that so the younglings don’t have a chance to form attachments to their parents (or anybody else) and be taught from the start to not be attached. The reason why they said Anakin was too old to be trained was because he was attached to his mother.
When it’s summarised like this you really get the sense of what total jerks the Jedi were turned into in the prequels. It’s funny how the characters portrayed as a child abducting, brainwashing, dispassionate, celibate cult are the heroes! I know this isn’t the thread for it, but it cannot be overstated how much all that stuff has to be cut from the prequels.