excluding multi-player / team postcards and cabinets, here's a few individual player postcards/cards that pre-date their established "rookie cards":
1909 RPPC in Superior Blues Uniform - Dave Bancroft:
1967 Cincinnati Reds Team Issue PC - Johnny Bench:
1955 JD McCarthy PC (postally used in 1955) - Jim Bunning:
c1943 RPPC in Monterrey Uniform - Roy Campanella:
1914 University of Michigan Photo Card - George Sisler:
1950 Coppedge Studio Winston-Salem Cardinals Team Issue - Earl Weaver:
__________________
...
http://imageevent.com/derekgranger
Working on the following:
HOF "Earliest" Collection (Ideal - Indiv): 250/346 (72.3%)
1914 T330-2 Piedmont Art Stamps......: 116/119 (97.5%)
Completed:
1911 T332 Helmar Stamps (180/180)
1923 V100 Willard's Chocolate (180/180)