How long have you gone before an oil change?

My neighbor back a few years ago bought one of my extra bikes I had a 2007 Kawasaki 900 custom and while he doesn't ride all the time he tends to go long stretches before maintenance.

I've always used either Amsoil or Motul synthetic in my bikes so he has always asked me for help when oil changes were needed since he's just one of those people that likes someone else to help him out when the time comes.

His last oil change was a year ago and about 4-5K miles and so I helped him today and changed the oil since the bike was getting a bit grabby clutch wise. I told him an oil change would likely help so he gave in and we changed the oil. Surprisingly the Amsoil still had some color to it and you could see light through it, but really had a strong gas contamination smell.

I'm guessing that was part of the problem since the oil may have been thinned out a bit from that. After the oil change the clutch was fine and the bike even started easier according to him. I told him six months max on oil changes but I get the feeling that advice will be ignored. I guess it's a good test of how much abuse a motor can take