A few seconds becomes a moment. Carefully aiming becomes "in the right direction" which he absolutely was. God your arguments are shooting around so fast from place to place hows anyone supposed to keep up it's like a magic trick. Reloading and firing is literally a measure of dexterity which you very commonly lose as you get older what are you even talking about.
Yes, you will at least need to take a moment to aim, but a few seconds is far from unheard of. Drill manuals of the period are extremely clear on this point, soldiers are always to load, present (read: aim), and then fire. The practice you're using, where the guy whips the gun into the air and fires off a round as soon as he possibly can is not how these weapons were used.
And I didn't say "careful aiming". I said you have to at least get it pointed in the correct direction. These weapons already have poor accuracy, if you have a barrel pointed a few degrees in the wrong direction you will not hot anything. The point of all these musket drills is not just to make the guns fire as fast as possible, it's to produce as much accurate, effective fire as possible.
As for age related dexterity, I'm actually going to drop that point because in my attempt to check how old that guy is, I actually found more about his background that makes the age thing irrelevant (also, he looks like he's in his early 50s or so, that's not exactly old and decript). He's not just some ramdom old guy. He's a massive fan of Ferguson and his rifle and literally wrotethe book about both, is a former member of the international muzzle loading team and has more that 40 years experience with this sort of thing. A trained competive shooter with decades of practice is in no way a representative example of what the average person, or even the average trained soldier, could pull off.