Being in my 40's and reading this, the only thing I can do is quote Tyson:
"Everybody has a plan until they get punched in the mouth." -Mike Tyson
"Everybody has a plan until they get punched in the mouth." -Mike Tyson
My advice from the other side is that there's too many unknowns to plan out your career. Fields shift in terms of content and culture, and you don't know what you like until you're really in the middle of it.
By a lot of metrics, I've achieved plan A, but found out, after a lot of work, that I am not a good fit for it and that plan B has a lot of similar problems. I never had a plan Z.