Credit report number

[Jim S.]

Does a young person (21 year old) start out with a credit report number in the 700's and work their way down with late payments and such or do the start out at 0 and work their way up "proving" their credit. Just curious how it works. Would it be unheard of for a 21 year old to have a high credit rating? How long does it take to build good credit from no credit or to change bad credit to good?