Need to overcome some obstacles

I am hoping to change careers at 43 from Administrative Assisting to nursing and sometimes I wonder if I have what it takes to get through school. I think I'd be a good nurse (LVN/LPN), just not sure about the student part; especially since nursing is one of the hardest programs out there. I have a few issues; stamina, learning skills, and time.

I have had cushy, sedentary jobs for the last 20 years and have very little physical energy or strength; I'm sure I'd find that within myself eventually, but I have never been an excellent student and I have to work full time. I need ways to organize myself and to overcome these obstacles; especially learning. I feel so out of my prime....Any suggestions for me?

Thank you in advance for your two cents!