Moose, you work up to it. I've done a few centuries (100 miles) and my normal rides are ~ 30 miles, so 40 isn't a big deal. However, it's a hard route we took. I finish a ride exhilarated and that feeling carries into the next day, but I was definitely a bit whipped last night.
Cycling is an incredible low-impact cardio workout guys. Best thing I discovered in middle life by a long shot... Super fun. Out in the clean air, seeing sights, covering ground, hauling ass. The "kit" for it is admittedly goofy as it gets.
Vek, I'm not a desk jockey, I've done the rural thing for 25 years. I should start adding some of the "stuff" that I do to my exercise reports. Gets pretty physical out in the sticks quite often. Anyway, it doesn't leave me feeling like I need to be lifting heavy things for sport.
Anyway, it doesn't leave me feeling like I need to be lifting heavy things for sport. 
