Well that does clear some things up, but does creat other problems. First I’m well north of 70 so age has nothing to do with it. How well you understand the operation of a small engine means everything in this case. Your first mistake was watching boobtube videos and believing that the person who posted knew what they were doing. Second, you didn’t know there was a difference between L-head and OHV engines which greatly contributed to the problem. Checking and adjusting valve clearance on an L-head engine is about 50 times harder for a DIY guy, than an OHV engine. That is why I never recommend the DIY guy’s attempt this, as you can cause expensive problems very quickly.
At this point I don’t know how to help you in this thread, because it has become so confusing with correct and misleading information. Trying to figure out which posts are good and which ones are bad is not something I want to attempt. Maybe someone else would like to try to tackle it. You’ll have to decide how you want to proceed, but as you said earlier, you might be over your head.