Wow, you’re good! 
My personal experience is far worse than yours.
SAME!
That’s one of the reasons I don’t golf.
Yep. It is rare to encounter true dimension lumber. The 2 x 4 is the raw dimension intended to be planed smooth to the finished lumber. The true 2 x 4s I have seen were all rough saw cut lumber. But I have worked on older homes that used the in-between dimensions, 1 5/8” x 3 3/4”. Pain in the butt trying to repair a wall.
I actually had grooved my swing pretty optimally sometime in my early 20’s, but my anatomy failed me in the long run, as my left leg is close to an inch shorter than my right, resulting in a reverse weight shift and when I missed it was a wide slice to the right. For about 2 years I kept shooting in the low 80’s, but that f. slice would come up at the worst times and I’d get that one bad hole which would keep me from breaking 80. My handicap leveled out as a result around 13, and when my father’s health prevented him from playing anymore, I stopped too as I got into other activities, and only found out about my leg when my GP pointed it out to me years later. I might take it up again this spring as some time at TopGolf a couple of years ago showed that the muscle memory is still there, and I am in better shape than I was back then too.