The history of firearms has a poignant feature where muskets and such, despite being inferior to longbows of the time, saw the fact that in about 24 hours you can be reasonably effective with a firearm where in 24 hours you are going to be nowhere with a longbow and maybe only slightly better with a crossbow or shortbow. I have to wonder if there is not something similar, or at least some kind of feature of keyboard and mouse*.
Alternatively everybody up until now uses a mouse so you have your few hundred hours of mouse use by the time you pick up games. I will be curious to see what happens when all the kids on raised on touchscreens but not mice (and if I count laptop trackpads as not mice we are maybe 3 years out from a sizeable number that pick normally pick up such games up at 7-9 years old). That said it will probably be balanced out by minecraft.
*I grew up before Doom (though Duke3d and Star Wars Dark Forces were probably the bigger drivers) and
http://old-computers.com/MUSEUM/photos/ResearchMach_Nimbus_Mice_s1.jpg was what I knew as a mouse for many years, oh and it was a ball mouse as well. Still had possibly a thousand hours in on it before then though.