The bike thing is the answer, Bill. If you do an exercise for the enjoyment of it, rather than a chore to keep yourself lighter, it's likely to remain a part of your life for a long time. But winter is coming...

Do you have something that the both of you enjoy that you can do indoors, through the winter? (Wipe that smirk off your faces, guys! ) Maybe squash, or badminton, indoor tennis, basically anything to keep you interested and active rather than rote exercise?