The problem you're most likely running into is that every type uses both S and N. You either use introverted sensing with extroverted iNtuition, or you use introverted iNtuition with extroverted sensing. They are different functional roles that occupy different cognitive space in the brain. The older you are, the more access you get to the weaker areas, so most types will exhibit N and S tendencies with a little work. This is why, quite often, old people are difficult to type correctly. You really should read up on Jung though, it'll make Myers Briggs make much more sense.