Can someone please tell me how old a dui has to be before most companies will hire you?

It depends on the company--most have to be anywhere from 5-10 yrs--the company's websites will usually tell you how long it has to be or if they will even accept them.

I went to a truck school and filled out the paperwork truthfully. Have you had any DUI'S within 10 years? Answer NO. Answered the same question for WERNER got picked up for orientation. After 2nd day and I had filled out ANOTHER application question was have you EVER gotten a DUI. I had 1 in 1982, A driving to endanger in 1983, and 1 more DUI in 1985. I have stopped my party habits I had in college, and have had a clean record ever since. Last problem was 23 years ago! WERNER let me go because the driving to endanger was a reduced DUI. They said they could waive two convictions but three was too many. I said you didn't ask what I was charged with, You asked what I had been convicted of.
Anyway I applied to US Express and they said if I could get 6 months of experience then they would hire me. I have found no company that is willing to hire me. I have given up on trucking and hope to get a job driving a smaller truck. Don't know if this helps but that's my tale of woe.

My son had one DUI over 5 years ago and one charge of minor consumption which will be 5 years in August. His first choice of a trucking company was US Express, but the cdl school he is at told him that US Express wouldn't hire him due to 2 alcohol related arrests. I personally called US Xpress and talked to 2 separate recruiters and was told the same thing. Their policy is you are only allowed ONE alcohol related arrest in your LIFETIME!! Very harsh in my opinion. People do make stupid mistakes in their youth, but I don't believe they should have to pay for them the rest of their lives!