If you can do anything other than magic, do that instead. If you can cast spells, and also enjoy math, become an accountant. If you can feel the density of magica in the air, but are also skilled at baking, become a baker. If there are any other paths in your life that would fulfill you, do those.
However, if you know down to your marrow that magic is the only thing that you wish to do, want to do, and will be able to think of doing... embrace it entirely. Immerse yourself utterly. Let it consume you. Breathe it, think it, know it. Be a vessel for magica.
Because to do it only halfway, to treat it as a "job", to play with it idly... that is the surest path to a life of regret and misery.
Also you will likely blow off an arm or turn your insides into some kind of glittering goo. Take it seriously!!
-Introduction to wizarding by the Prime Wizard at the Grand School of Magica