Some guy on twitter started arguing with someone about Jason Heyward vs. Starlin Castro and I had to get involved. I did some digging using the B-R index and brought up the only 20-year-old players to walk over 55 times and have an OBP over .365. The list of players are, in order of OBP: Ott, Williams, Kaline, Foxx, A-Rod, Mantle, Heyward, Robinson, Griffey.