A misdemeanor will be on your record for life if you are convicted or plead guilty. On a job application you are responsible for revealing this information. Whether you use a fake ID to purchase alcohol or you loan your ID to a minor, you can be guilty of a misdemeanor. If you loan your driving license you could lose it for 6 months. However, if your BAC is .10 or higher the consequences increase to those of 21 or over.
Most states have a similar law in effect.
If over 21 a blood alcohol concentration of .10 of higher is enough by itself to establish you were driving under the influence. Between .05 to .10 BAC you can be arrested for a DUI but additional evidence will be needed to establish your driving was effected.