I do not like it when someone has adventures that a level 20 wizard would have, and them to join my party... not even knowing magic missile. Gale has an artifact level magic item on him, a huge history, has had sex with god herself... and its like "pew tiny bolt of fire"
nobody in this group should be level 1, unless the tadpole has already eaten our brains and the tadpole just thinks its the people whose brain they have eaten...
If anyone came to my table with these backstories, except maybe shadowhearts... I would say "no, dial it back a little, you are level one"
Why should he know magic missiles? O_o
He could be Arcanist ...
Using his Intelligence and talent for magic to simply study lore about spells, magic items, eldritch symbols, magical traditions, the planes of existence, and the inhabitants of those planes.
He could be Historian ...
Studying lore about historical events, legendary people, ancient kingdoms, past disputes, recent wars, and lost civilizations.
He could be some kind of Nature sage ...
Studying about terrain, plants and animals, the weather, and natural cycles.
Or Religionist ...
Studying about deities, rites and prayers, religious hierarchies, holy symbols, and the practices of secret cults.
And those are just options purely based on Itelligence description.

I bet we could find many more options among mages wich simply dont have acess to destructive magic, since they never needed it.