I wouldn't be worried about it yet. Middle kid didn't skip numbers, but at age 2-3 she always said eleventeen, no matter how many times we told her that was not a number. She had some other odd stuff going on too - she mixed up opposites, most notably hot and cold, until about age 6.
As I have mentioned at other times, we did not think this kid was advanced, and I declared her "not college material" when she was 4.
Middle kid is now a HS senior, awaiting college admissions decisions. Has two acceptances, both with merit, one is full tuition. She is NMSF (should be NMF soon) and she is taking Linear Algebra this year in HS. She figured out the eleventeen thing.
