Well, I'm bored, so let's take a look at CQ's top ten.
(I'm disregarding month of birth when calculating ages because meh)
1. Evans
Won the Tour of Austria and the Brixia Tour in 2001, age 24. Breakthrough in 2002 but no really big wins until the 2006 Tour de Romandie. Former MTB rider.
2. Contador
Won the Setmana Catalana and a Tour de Romandie stage in 2005, age 23. Breakthrough in 2007 (Paris-Nice, TdF).
3. Gilbert
Won the 2004 Paris-Correze and several similarly smallish races in 2005, age 22-23. By 2006 he was contending big races everywhere (some of his victories: Het Volk, Dauphine stage, GP de Fourmies), breakthrough in 2008 (Het Volk, Paris-Tours, 3rd in Milan-San Remo, etc)
4. Samu Sánchez
No great results until 2003 (age 25), even then no victories but he became a contender in hilly classics (LBL: 6th in 2003, 4th in 2004). Breakthrough in 2006 (age 28) when he won a Vuelta stage and the Züri Metzgete and was 2nd in Lombardy and in the Fleche.
5. Joaquim Rodríguez
Won stages in the 2003 Vuelta and Volta a Catalunya (age 24). By 2008 he was a solid GT and hilly classics rider, but the real breakthrough was 2010.
6. Cancellara
By 2003 (age 22) he was winning TTs at top level races (Tour de Suisse, Tour de Romandie). From 2004 onwards he was a contender in the cobbled classics and by 2006 (age 25) he was the best time-trialer in the world and had just won his first Paris-Roubaix.
7. Greipel
Before his breakthrough in 2008 (age 26), when he won a stage of the Giro and a truckload of other races, he hadn't done much other than be a decent sprinter.
8. Vinokourov
Turned pro in 1998 (age 25) becase Kazakhstan is pretty far away, started winning rances straight away and by 1999 he was winning stuff like the Dauphine. It would have been interesting to see his development if he had arrived in France at 20 or so.
9. Farrar
Didn't get many results until his 2009 breakthrough (age 25). Maybe a trend with sprinters, Cav be damned.
10. Gesink
The guy won the Settimana Lombarda at age 20 while still riding for Rabobank's development team for god's sake. Relative breakthrough in 2008 (age 22) with many very good results (4th in Paris-Nice, 4th in the Fleche, 7th in the Vuelta, and oh, is that a 10th in the Olympic games frickin' TT?) but his 2007 season was very good already.