Hi, just started taking lessons. I'm 62 this month, and my sensei is fine with me not being able to do seiza. No, not lack of willpower, willingness to overcome pain, blah blah blah- knee is a replacement courtesy of military service and it does NOT bend that far, period, end of story. Is this going to be a barrier to making progress? Arms and wrists are still fine and many years of bladesmithing have helped here.