Complex sentence: When Swatton was 7, he would refer to himself as a "Gem Hound" or "Pebble Pup" and by the time he was 15, he had moved on to Silversmithing.
Split into simpler sentences: When Swatton was 7, he would refer to himself as a "Gem Hound" and "Pebble Pup". When he was 15, he had moved on to Silversmithing.