Just been looking up the stats...
Of the four riders who have previously won the points competition in all three grand tours:
Abdoujaparov did it by winning the Giro points jersey in 1994, aged 30.
Jalabert did the same in 1991, aged 31.
Merckx completed the set by winning the Vuelta jersey in 1973, aged 28.
Petacchi was 36 when he finally won the Tour green jersey in 2010.
So if Cav were to win the red jersey next year, he'd be the same age as Eddy Merckx was when he won it (admittedly, Merckx had won more overall by the same age, but still... not bad).
No one has won all three in the same year. Abdoujaparov won the Tour/Giro double in 1994, Merckx won the Giro/Vuelta double in 1973. Four riders have won the Tour/Vuelta double - Altig, Janssen, Kelly, Jalabert. I can see Cav joining this elite group one day, though probably not this year. Who knows - maybe he could become the first to win all three in the same year? Unlikely, but you never know.
Only three riders have won stages in all three Grand Tours in the same year: Miguel Poblet (1956, aged 28), Pierino Baffi (1958, aged 28), Alessandro Petacchi (2003, aged 29).
Anyone care to bet against Cav becoming the fourth rider to achieve this feat this year, thus becoming the youngest person to do so? I suppose it depends whether or not the team enter him in the Vuelta, but you'd think he would want to do it this year of all years, while he's World Champion.
Cav is still some way off the best when it comes to overall number of points jersey wins, but I reckon he'll one day catch Jan Janssen and Djamolidine Abdoujaparov at least - they won five GT points jerseys each. Merckx won 6, Jalabert 7, Kelly 8, Zabel 9. He may or may not catch any of them depending on whether he develops more into an all-round points chaser à la Kelly and Zabel, rather than the specialist stage winner he is at the moment. Though I can't really see Cav ever winning a Grand Tour outright like Kelly.
If he can extend his career as long as the likes of Ale-jet and Zabel, who knows what he could acheive...
d.