I forgot those tidbits. Thanks, but still think maybe her age was pushed a bit. Excalibur was 125 issues, and sometime around or before #50, she had been given a car but was not legal age to drive it (although UK driving laws may be 18 rather than the US 16, so I may be waaaay off base there.
But standards (acknowledging that Kitty's timing could very well be off seeing she did not attend regular schools) would put the sophomore year at 19-20, hence my further confusion.
With further thought, 21 does make sense as there have been a couple SIX MONTHS SINCE LAST ISSUE skips in Marvel continuity over the past few years.