For more anecdotal evidence, I've admittedly only had my lamb jacket for a little under 2 years at this point, but the only thing that has done any lasting damage to it is my cat. He managed to put a tiny puncture in it when I was dumb enough to hang it from a door knob, and there is a nearly invisible scratch on the sleeve from his back claws that we are too lazy to trim. So basically as long as you don't take a knife to it you should be fine.
It does have some noticeable lighter coloration where it rubs frequently (elbows and where my messenger bag strap rubbed on the hem) but I'm pretty sure I could darken those up just by conditioning. Either way it definitely is character aging and not what I'd consider damage, though of course it's still not going to be bomb-proof like a calf or FQHH would be.