What is the most dilated you could be to get an epidural?

Women do not have to wait until they are dilated to a certain level before they can ask for, or receive, an epidural. According to the ASA's (American Society of Anesthesiologists) current guidelines, "patients in early labor should be offered the option of receiving neuraxial analgesia (spinal or epidural) when the service is available, and it should not be withheld to meet arbitrary standards for cervical dilation." If a woman is in active, established labor, and is uncomfortable, epidural analgesia is the most effective method of pain relief. There is no medical reason to wait for a specific dilation target.

Source: http://www.lifelinetomodernmedicine.com/ArticlePage.aspx?ID=302a85f8-7135-4174-bd4c-2bc4ad7e04c2&LandingID=fc6eb1da-98e4-43c7-bb9f-09c17e2a005d

In additioin, some places wont give epidural if you are too advanced in the labour as the baby could theoretically be born before the epidural is administered and kicks in so there is little point.