Nadal won his first slam at age 19y1w earlier than Pete won his first slam at age 19y1m.
It is general consensus that Sampras is more talented than Agassi who didnt win his first slam until he was 22 and won 5 of his 9 slams after that age of 29. (while it may disputed, I still think that Michael Chang is the most talented player in history)
in April 1993 when Pete reached #1 ranking for the first time at age 21, this was his recrod at the time, and he has acompplished much more than Roddick/Aggassi did at age 21 without question.
Slam - 1 (US Open)
Master Cup - 1
Masters - 2 (Cinncinati, Miami)
Titles - 16
at 20y3m and now #2 in the world
Slam - 2 (French Open)
Masters - 6
Titles - 17
(for comparison: Hewitt in June 2003 @ age 22, the last time he was #1)
Slam - 2 (US Open, Wimbledon)
Master Cup - 2
Masters - 2 (Indian Wells)
Titles - 19
It seems that Nadal has achieved more at his age, except for the ranking.
While he has not achieved #1, he has surpassed in achievement than Sampras and Hewitt at their respective age. Talent is pointless as some may suggest, but if Nadal keeps this up, he may well surpass Sampras.!
and still rank #2.