Stephen, I'm not a professional trainer but I think you do bring up a good point about applying principles to practice. You are 60 years old and have certain realities to deal with. If an 8kg jump is too big for you then a smaller one might be appropriate. At 60 years of age just staying active is probably a good goal. You can get a lot done with a 24kg kettlbell.
I just turned 50 years old and I'm wondering whether the Sinister standard is realistic for me. At a certain age we just have to deal with certain physical realities. At some point just staying mobile and healthy will probably be more important to me than hitting certain weight and rep standards.
Best of luck