Arraez finished his regular season hitting .334 in 366 Plate Appearances. He turned 22 in April.
The entire list of players since 1961 who hit for as high an average over as many plate appearances in their age 22 season (defined by Baseball-reference as still being 22 on June 30):
Alex Rodriguez 1996
Vada Pinson 1961
That's it.
Continuing the list back to 1901 (formation of AL) -- fun to look at.[And I had forgotten Williams was only in his age 22 season in 1941 when he hit .406.
Al Kaline 1955
Stan Musial 1943
Pete Reiser 1941
Ted Williams 1941
Ted Williams 1940
Charlie Keller 1939
Joe DiMaggio 1937
Roy Weatherly 1936
Jimmie Foxx 1930
Mel Ott 1930
Jimmie Foxx 1929
Lloyd Waner 1928
Freddie Lindstrom 1928
Lloyd Waner 1927
Heinie Manush 1923
Tris Speaker 1910
Ty Cobb 1909
Eddie Collins 1909
Ty Cobb 1907
Jimmy Scheckard 1901