What age do my child have to be to use trust/settlement money to get a car ?

A trust is controlled by the terms of the document that creates it; there's no such thing as a standard trust that is spelled out in the law. What that means is that no one can tell you what kinds of distributions are permitted from your child's trust without actually seeing the trust document. In general, it would be fairly common for a trust for a person to allow for something like the purchase of a car for that person; but that does not mean that your child's trust permits that kind of distribution. Find an attorney who is experienced with trusts and have that attorney review the document that controls the trust. That's going to be the only way you can actually know what it allows. Best wishes to you and your child.