A: I want to leave home, mum.
A: I am a grown-up, and I can stand on my own feet.
B: It is all up to you.
stand on one’s own feet
e.g. I hope he learns to stand on his own feet someday.
e.g. Whatever a man's status may be, he must have an aim. If not, he can hardly stand on his own feet in the world. That stands to reason.
e.g. If he doesn't stand on his own feet at his age, he'll lose his self-respect.
e.g. Websters want someone who can stand on his own feet.
stand on one’s own legs
e.g. I tried to stand on my own two legs rather than turn to my parents.
e.g. I don't want allowances made for me. I want to stand on my own legs for what I'm worth.
e.g. When I was eleven my mother died. After that I had to stand on my own legs and earn my own living.
be up to
I don't feel up to any more work today.
Michael' s not really up to that job.
Your behavior does not come up to the expected standard.
Your work does not come up to the requirements.
It was up to the local authorities.