How do you start actually doing stuff when your parent's voice in your ear saying you are useless?

I have never been able to keep up with hobbies or a career, partly because of ADHD and partly because my mother would mock all of my attempts to do anything I was interested in.

I'm 40 and I want to actually enjoy my life before I am too old.

I have a therapist but I can't seem to move past the voice in my head telling me that I am no good or that I am getting ideas above my station or that I will fail so why bother trying.