Prime has no other meaning than your expectations of success and when you've achieved them. Getting to know yourself and being comfortable with what it is that you want to do is the most important thing you can do in your life. Worrying about your "prime", sounds more like buying into a hype cycle than anything.

On a personal note, every step of my career has been forward and also unexpected. What I envisioned myself doing and what I ended up doing were two different things. And yet I'm happy and successful. Age 41.