Squats and deadlifts are the king for boosting T. Gotta work those big muscle groups. So ditch all those isolation exercises designed to add that extra bump on top of the bicep for a competition bodybuilder and get back to the basics of what make people strong. Presses, pull-ups, and squats.
I find that what slows down as I get older is recovery time. Short intense workouts seem to work better for me as well. Of course, like lots of us, I'm now feeling all the injuries I inflicted on myself when I was younger. Ahh, to be young, elastic, and invincible :P