[lutorm]

That makes no sense. Looking at that Wikipedia article, it says lift L=0.5 rho v^2 A C_l. For flight, L = mg. So for a given speed you get a criterion on the density of the air:

rho = 2g/(v^2 C_l) * (m/A)

So the density at which you can fly depends on the surface density of the structure. Which of course makes perfect sense -- if you build a lighter airplane, it needs less lift.

To get that altitude, Karman must have used some typical surface density of an ordinary airplane at the time. Presumably we can now build much lighter structures, so we should be able to fly higher.