Feniurme
In Nasverus, Gaia began to suppress the mystery after the Age of the Gods, which means that in the Age of the Gods there should be no opposition from her. Also, Emiya's powers in the Age of Gods shouldn't be limited to Blades only! He was limited to the Blades only because he did not have access to the mystery and the only mystery available was in his soul origin. In the Age of the Gods, he should be able to create any thing in his subconscious, like in Harry Potter with Occlumency. Also, in the Age of the Gods, it seems that there were no magic circuits, there was something more advanced and magicians used Ether, not Mana. Aether is much more powerful, even as a child, Bel should not have problems with tracing, because Emiya had an incredibly low amount of Mana and that was enough for him!