Each weapon have a Skill requirement and a Strength Requirement.
If you do not meet the requirement you will have a penalty to performance. Though I am not sure what the exact penalty is. I think not meeting the strength requirement is a penalty to accuracy. Not meeting the Skill requirement is a penalty to damage.
For Example a Hunting Rifle (IMHO the Min Weapon to use on a death claw) needs Guns 50, and Str 6 to reach optimal performance.
[Edit]
Unlike Fallout 3, enemies in the game does NOT scale to your level. So there is a thing called too low level to goto that area

If you are trying to head to New Vegas, go the route the story tell you to take. Do not go through the Death Claw infested area to the north of Goodspring.