Feeling tired should almost never be an excuse, because your body has huge reserves of energy. But if you eat badly, stay out late, drink too much, and so on, you'll pay a price on the course.
My dad was a good athlete. My mom had longevity. There were some athletic genes that certainly got passed down.
Yes, I applied a lot of what I did in football to golf.
Early in my career, my 3-, 5- and 9-irons performed differently than my other irons. But I adapted and made them work.