Thanks for your input, everyone. This is one of the major reasons I love aikido in general: everyone I ask for help or advice usually rushes up to help.
I think I will pick up some of the literature mentioned by Erik H. on the subject and scout out some local gyms, mainly to speak to the physical fitness trainers as Mayland Long did. I'm leaning towards a home gym set just so I can encourage my wife to excercise a bit with me also. Lean muscle mass with good flexibility is the way I do want to go. The consesus agrees with my sensei as to the positive efeects of weight training. Again, thank you so much everybody!