After a slow start (6.20 ERA through April), Mat Latos (Padres) is currently the only pitcher in the entire league with a WHIP below 1.00, an ERA under 2.50 and more than 100 innings pitched. He is in his first full season as a starter in the ML and is only 22 years old, not too bad for an 11th round pick in 2006.
He has also been the Padres (leading the NL West and best team ERA in ML) best starter, and could easily be a Cy Young contender for years to come.
2.50 ERA or lower, 1.00 WHIP or lower, 123+ IP (by age 23, since 1910)
1910 Walter Johnson (Senators, 22)
1914 Ernie Shore (Red Sox, 23)
1914 Dutch Leonard (Red Sox, 21)
1968 Tom Seaver (Mets, 23)
1971 Vida Blue (A's, 21)
1976 Frank Tanana (Angels, 22)
1985 Dwight Gooden (Mets, 20)
1986 Roger Clemens (Red Sox, 23)
2010 Mat Latos (Padres, 22)