First played tennis aged six alongside his dad and two brothers He began playing at the Club Internacional de Tenis in Paraguay's capital city Asuncion Was a sparring partner at the 2022 Nitto ATP Finals His two brothers both played college tennis in the United States

Trained at the Rafa Nadal Academy from 2022-2023

Won first ATP Challenger Tour title in March 2024 in Brazil

Aged 19, Vallejo became the youngest Paraguayan to win an ATP Challenger Tour title