Baldur's Gate 1 question...

Why is it that when one of my characters level up I cannot allocate another proficiency point in a weapon skill. For example, Imoen has two points in Bow proficiency. I have a point to allocate but I cannot add it to Bow so I add it in another proficiency that I would never use. It seems like a waste. Or is there a level requirement that I need to satisfy before I can allocate another point into Bow?

The reason for that is that imoen is a thief and as such can only allocate 1x point into any proficiency.
Thieves and mages only get 1x point, Cleric/Ranger/Paladin get 2x points and warrior gets 5x.
You might want to check the manual as all theese rules etc are explained in detail there.

Ah I see, thanks Biff.