Driving fitness can be impaired by the following: fatigue, ill health, distractions in the vehicle, drugs/alcohol, emotions (anger, sadness, fear).
If you drink alcohol, it will impair your ability to drive.
Yes. Most definitely.
It depends. Any substance, such as alcohol or drugs, prescription or otherwise, that influence/impair your driving can violate state laws. The idea is that if you are not safe to drive you should not be driving. It's an issue of public safety. If you have something in your system that COULD impair your driving, then the next step is to determine if it DID impair your driving. A few ounces of beer with a meal would probably not influence/impair your driving. As you increase the concentration you make the influence/impairment more likely. Same with drugs. The short answer, low dose, less likely to impair, high dose, more likely to impair.
No, weed doesn't impair your ability to drive like alcohol does.
impair=hinder, impede
Drinking a sufficient amount of alcohol can impair driving performance, thus increasing the risk of an accident.
If you want to hit things... then sure go ahead
Too much marijuana will impair your vision. Only a little bit will impair your judgement.
Some can, some can't. It depends on the drug. This will be indicated on the label, but consult the pharmacist for details.
The unbearable stench in the air seemed to impair her senses.
The accident will probably impair his good arm.
Age doesn't really matter, it's just that some old age related ailments that some get impair their ability.