Complex sentence: David P. Flores (US) infiltrated the Boryokudan group in 1992 the first american to do so at 21 being the youngest foreigner to be inducted into a japanese Yakuza crime organization.
Split into simpler sentences: David P. Flores (US) infiltrated the Boryokudan group in 1992 at age 21. He was both the first American to do so and the youngest foreigner to be inducted into a Japanese Yakuza crime organization.