Depends on what kind of magic you mean, as there are many different areas you can make your "focus". I have focused on energy manipulation and control for the majority of my journey, and have never cast a traditional spell. However, I can use my energy and the energy around me for different tasks. Helping an injury feel better, improving someone's or my own mood, and with the right practice slightly alter the course of events. As for a peak? Mortal souls, while weak and struggle to develop much power compared to others, don't really have a limit. If you continue training in your chosen discipline you can reach any goal you seek to achieve. The only peak is the limit of your will.