Complex sentence: In 1991, Najjar made his senior international debut and became the youngest striker of La Sagesse first team while still playing in the youth league, the fifteen years old he was chosen to participate in some of the first team toughest games in the Lebanese Premier League.
Split into simpler sentences: In 1991, Najjar made his senior international debut and became the youngest striker of La Sagesse's first team while still playing in the youth league. The fifteen-year-old was chosen to participate in some of the first team's toughest games in the Lebanese Premier League.