LOL!! Dive on in!! I STARTED training at 41 in the worst shape of my life. Wrestled in high school all those years ago but thats it as far as anything similar goes. Going strong 2 yrs later.
Since you've done this before plan on it sucking for about 3 weeks. Start slow and remember that you don't have to keep up with the 20 year olds. Also, plan on injuries taking alot longer to hear than they used to. I bought Aaflac accident insurance and it turns out that was one of the best decisions I've made. I get paid every time I pull, twist, or torque something. It might be worth looking into as a just in case...
Good luck and welcome back to the game.