you could always try DeviantArt's Resources, go to model>male>anatomy>nude and then search "old man"
but also that is precisely why I just pick ONE person to obsess over, so I don't have to do any creepy searches for references, because I would probably search: "Male anatomy" "man lying down" "Six packs" :I
Wow, I tried as well, all my searches ended up with primarily young woman and boobs as well as pervy old men admiring those women.
Unrelated note, I had a dream that I just drew another webcomic and it looked amazing. Yes the plot of it was incompressible and boring as dreams often are when you wake up, but the characters were all wearing gas masks which always makes things a win.
I noticed that my early hiex pages have a lot of white void in it. I kind of.... Drew some simple backgrounds in them (someone once told me that adding something as simple as a line to represent the floor or wall corner makes a big difference). May upload them soon.