''Because I'm in my 40's and think I'm never going to find out now.''
That is SO untrue!
I am nearly 42, no athletic background, never did any sports, running occasionally but even when I ran a lot I didn't feel fit and healthy.
I found CrossFit last year and it changed my life, learning how to train with variety across different fitness domains (strength, speed, endurance, flexibility, stamina... etc) and across different time domains at high intensity - this is what makes our bodies healthier, fitter, stronger, not specialising in one movement for ages. I did my first CrossFit competition four weeks ago, and competed again yesterday in a team of 4 athletes. In the competition there were athletes way over 50 who were absolutely killing it!
One year on, I have a 55kg clean & jerk, I can squat clean 60kg, and do 10 unbroken kipping pull-ups. I have lost a dress size, but I don't want to be thin, I just want to be able to lift more, run 100m faster, and get my first muscle-up on the rings.
Google CrossFit, you don't have to be fit, or thin, or young to start, you just have to start. The team spirit and camaraderie is amazing. You'll walk in terrified and walk out accomplished. And when you get a sub 5 minute Fran send me a PM!