What do you call someone, or someone's point in life when their children have moved out and they have more time, or are willing to make riskier career choices?
This identity is independent of career, educational, or professional milestones, however. Becoming an empty-nester does not necessarily mean one has more time or is willing to switch to a riskier or less remunerative occupation.
In terms of taking more risk with their career choice, a person who's fulfilled their financial obligation to their children and who's nest egg is comfortably lined can be called, depending on circumstances and age, by many names. However what you are describing is someone who's pursuing a "2nd career".
I Googled "2nd career" and got 224,000,000 hits. It is a phenomena that is being written about by financial and investment institutions and educational and retirement advisors as well.
"Encore Career" is also being used for this concept but to a lesser extent.
(What I could not find was a single word to call a person pursuing a "2nd career".)