Fages played a key role in Saints' winning try in their 28-24 victory at Catalans Dragons on Saturday and Cunningham was delighted with the 22-year-old's performance.
Cunningham says the former Salford man is already a star in the St Helens side but he feels Fages can become even better.
"Theo has been brilliant since he came to the club," Cunningham told the St Helens Star.
"You forget how young he is, he still has lots of learning to do but he's already a top player for us. Not only does he set up the match-winning try for us, but he scrambles at the end to make a defensive play and saves a try."