KidSnide said:
You can create any number of justifications for this type of character. A weak, arthritic fighter could be an elderly master of a forgotten fighting style, and there are tons of examples in westerns where the clumsy drunk is the deadliest shot in the west. Young and naive clerics and idiot savant wizards are also classics of the genre.
You can legitimately question whether these character types are realistic. (I have it on good authority that small, elderly martial arts masters go flying when they are kicked in the chest by larger, younger martial arts masters.) In a more "realistic" game, a GM might want to limit characters that are exceptionally poor in the relevant areas. However, these are clearly legitimate concepts for a large number of games. I don't see why the rules should keep them from being playable.
But is this a role-playing question or a mechanics question?
I say my fighter is 60, but has great experience and tough as nails. Do I go with low physical scores, or decent one, and RP the difference? (my back!). In mechanic terms, if your charecter has a low str or dex, he has to be bad at something. He has to not be able to wear heavier armor, or not climb well, or get hit often. There has to be a mechanical implication.
The drunken fighter or shot is the same thing. He is clumsy when it doesn't count or the player feels like it, but not when it counts (think of him stumbling across a tight rope). Or the "idiot" wizard who know everything on arcana, the young cleric that has an uncanny sense of things...
You should be able to RP a concept you want, but that doesn't mean you have to mess up the mechanics to do it.