As Lightningmate has pointed out, a healthy young person greys, then blacks out out around 3-3.5g. Incidentally in a centrifuge with g gradually being increased following the loss of colour perception and encroaching tunnel vision, one can actually be fully conscious with a total vision loss before actual loss of consciousness occurs.
A higher g tolerance in a young person could actually be a very bad sign since one's tolerance is partly dictated by the elasticity of the blood vessels. Thus we older individuals often have a higher g tolerance as arteries harden with increasing age.