He joined UNAM at the age of 16, and was administered to Puma's youth sub-17 squad, as well as his twin brother Marco Antonio Palacios, a defender.
The passage describes how a person named (presumably the subject of the text) joined UNAM at the age of 16 and was placed on Puma's youth squad, along with his twin brother Marco Antonio Palacios, who also played for the team as a defender.