If you look around, you may spot there's a decent number of people over 30 (and 40) who have turned around their lifestyles and become very physically healthy. I'm one of them, having experienced mental illness like you - and I keep noticing others who have done the same as me. It did take a change in my mental health to help me get the kick start, but then the exercise (especially moderate weight training) put me in a positive feedback loop and improved my mental wellbeing to the point where I'm shocked at how 'normal' I have managed to become.

Good luck with getting back to better health.