Well, I'll let you guys take some votes on this. There is some rules options in the Advanced OSE book, and while we've been pretty good at staying out of the weeds as far as straying from B/X R.A.W., I've also allowed for Race/Class options from OSE Advanced, so I'm good with letting you guys decide.
Personally, I don't see how the wizard realistically can't swing something, that doesn't make sense. So at the very least, I'll say any character can use whatever weapon they want, but there will be a -2 penalty to your attack rolls to use them if their not something you're supposed to be using.
The second option, if we want to incorporate more of the OSE Advanced stuff in besides character Race/Class options is the idea of allowing Magic-Users to wield staffs:

So basically, if the Wizard was fighting with a dagger or a staff they don't suffer the -2 penalty.
The final option, if we really want to let the OSE Advanced leak into the campaign is to just straight-up let you play with the Weapon Proficiency rules of OSE Advanced:
We could retroactively allow you to pick weapon proficiencies as if you had at character creation. Or we could say you have the option of selecting a weapon proficiency at Level 2.
What is everyone's thoughts?