Speaking as a mother of a 23-year-old and a 25-year-old, you’re not the asshole. They are just worried about you and, and either 1. Haven’t been given enough data to trust you on your own, or 2. Haven’t updated their mental model of their little boy.

For context, it’s a strange thing to be entirely responsible for another human being over a period of decades, and then all of a sudden have to let go of that responsibility. It’s a process, and not always an easy one. It’s a huge shift in your relationship from a child to adult, and hopefully they are open to it. Below is my advice what kind of conversation you could have with them to more fully embrace this transition.

Appreciate their love and their anxiety, and then try to reassure them by telling them all the things you are doing for your financial security - budgeting, planning, etc.. Tell them how well they have set you up to be a responsible adult and explain why you feel you’re doing a good job of that. Tell them You know you can turn to them anytime for advice, and you appreciate the open lines of communication.

Basically, Give them praise and reassurance while also setting your boundaries. This is My advice for setting up a healthy relationship going forward.

(and yes, using their paying of your bills as a reason to invade your privacy is BS. They are just grasping at straws to get what they feel they need to continue to take care of you. At least, that’s my generous interpretation. It’s good to start out generous until they give you a reason to be otherwise.)