Just judging on the video and photos, the starter is turning the engine over each time and the level of wear is 'normal' and should not be of too much concern (I've seen worse). I think the first go at starting, where the starter disengages and 'whirrs' is not that usual (it seems the engine might fire, spin fast and chuck out the starter pinion, but then fail to start. Look at your timing.
On a different point, I tried to count your starter pinion teeth - counted 8. For your vintage it should be 9. I could have counted wrong. Also you may have a flywheel suited to an 8-tooth starter (unusual). If your starter and flywheel are mismatched then that could be an issue (I don't know the symptoms of this as have never come across it before.
And finally, does your starter have the front triangular steady bracket?
