Complex sentence: He was signed in 1998 but never really made a breakthrough onto the first team, being loaned to gain experience from ages 20--21 to another two northern sides, S.C. Salgueiros and Sporting de Braga.
Split into simpler sentences: He was signed in 1998 but never really made a breakthrough onto the first team. Relatively young, he was loaned to gain experience, to another two northern sides, S.C. Salgueiros and Sporting de Braga.