Shohei Ohtani began playing baseball in the second grade of elementary school and joined a Little League at an early age, where he experienced hardball baseball.

Even then, he was fast and capable of throwing powerful pitches.
Still, the older boys were clearly more skilled. They handled catch with ease and hit Ohtani’s pitches back solidly.

Facing these older players, Ohtani naturally developed a sense of rivalry.
He remembers thinking, “I don’t want to lose,” and throwing himself into practice with that feeling in mind.

Looking back on that time, he recalls:

“Maybe I felt frustrated about getting hit. But more than frustration, I think I felt excited and couldn’t wait for the next weekend.”

Over time, Ohtani grew to compete on equal footing with older players, gradually displaying abilities that stood out as exceptional for a child his age.

Placing himself among players who were better than him — in an environment where the level was higher — was essential to his growth.
The same principle later guided his decision to aim for Major League Baseball: to test himself where the competition was strongest.

Source

This quote comes from a Japanese book published in Japan and is not currently available in English.

Shohei Ohtani: Baseball Soaring Years I – Japan 2013–2018, p.258