I'm going to talk to like I would if you were one of coworkers.....
Baby bye. You want to become an NP, then go and become an NP. Do you know how many people return to college in their 60s, 70s, 80s? Do you know how many of age people continue to work until literally the day they stop breathing. Retirement is not what it's cracked to be for you because that's not what you want to do. If you have decided to use your savings, so what, you'll make that money back.
There are many things that you can do as an NP that don't require you to be on feet all day. My only question for you is have you decided what are you want to specialize in and what are you waiting for?
Here are your options you can go back to school and do something that you want to do or you could spend the rest of your days singing your should've, could've, would've(s). Just don't let age and your fears stop you. You've got this!