What are my options if my mom says she is going to keep my inheritance in a bank account under her name even after I turn 18?

Your options with respect to the inheritance that you are writing about depends upon from whom it is from and if the inheritance is to be held in trust by the express provisions of the Will or trust that gave you the gift. As such, you need to carefully read the document that gave you the inheritance with respect to when you are entitled to receive it.

If there is no express age limitation stated in the gifting document for your inheritance, then under the laws of all states in this country you are entitled to the gift when you are an adult, namely age 18.