(There were three "Robert Flynn" players around this time; this is Robert Joseph Flynn, born in 1942.)
Flynn signed with the Kansas City Athletics out of high school and spent his first season with Visalia in the California League. He was an unexceptional 4-7, 4.84 but was still one of 50 teenagers in Major League camps in the spring of 1961, as profiled by
this article, which notes that Flynn struck out 102 batters in 106 innings.
Flynn was also considered a prospect as an outfielder (hence some of the poses) but he never played there professionally, save for 10 games as a defensive replacement with the 1965 Birmingham Barons.
Ironically, although Flynn was profiled in the March 26, 1961 "teen prospects" article above, he had already been sent out, as noted in
this blurb from the day before.
(Off-topic, but if you click that link, you will find, right next to "Athletics Send Nine to Minors" an AP article called "Young Pitching is Hope of Cincinnati Ball Club", the not-very-enthusiastic preview of the Reds' hope for improving on their 6th-place finish of the year before. The 1961 Reds are one of the true overlooked "miracle" teams, as Bill James has noted, and for anyone who has read
Pennant Race [Jim Brosnan's diary of the season], the palpably perfunctory preview is perfectly pleasurable. [/annoying alliteration])
Flynn continued to pitch in the A's chain, never really achieving much because he just gave up too many hits. I get the impression that he had a fastball, and not much more. Best year was probably 1963, when Flynn went 9-5, 4.14 for AAA Portland, but still with a 1.57 WHiP. Just too many baserunners. He ended up back in the California League and was cut after posting a 1-2, 8.00 mark in six relief appearances for the 1966 Bakersfield Bears.