Capacity

Your magic capacity depends on the character.

How much they have studied magic, how much magic their parents could handle and they inherited, and their physical health.

For those who are new to magic completely:

magic capacity is the amount of magic one can handle before it starts to deteriorate or ultimately kill them.

I expect everyone to be logical about this. If the character is very sickly and was never taught magic at a young age, they are gonna have a low magic capacity.

Someone can only have so much magic. Once someone has filled their magic capacity, they will have to expel some aura of a type of magic before they can go and learn another one.

There is not a magic capacity for each type of magic, the character has a general magic level, and the only way to make it bigger is to practice and study.

Learning magic is like exercising, it takes time and consistency to get stronger.