While this is true, everything is not cast in stone, people are changing positions and opportunities are rising. The org structure in most places is dynamic, additionally leaders usually happy to delegate their responsibilities.
The growth into managerial roles happens kind of naturally, take more responsibility - become a team lead, take even more responsibility become some sort of manager. It has less to do with knowledge or diplomas more with the desire to take responsibility to be a leader and take responsibility for the others. The only limit here is the amount of responsibility you can handle.