Congrats! I made a similar life change a year and a half ago. I hit 40, was lazy, ate like sh!t, and had never really worked out.
So I walked into the nearest Cross Fit gym and signed up without knowing anything about it.
I'm now in the best shape of my life.....by far! I'm definitely not the strongest guy in the gym (not even close), but I have learned so much about Olympic weight lifting mechanics, gymnasitics, and diet.
I start my next 5 week nutrition challenge on Mon. Time to eat clean!