We don't have synonyms for gremmie yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are premmie, grimmie and grammie.
(n) :
(surfing, skateboarding, slang) Alternative form of gremmy (“a young or inexperienced surfer or skateboarder”). [(surfing, skateboarding, slang) Synonym of gremlin (“a young or inexperienced surfer or skateboarder”).]
(n) :
(surfing, skateboarding, slang) Alternative form of gremmy (“a young or inexperienced surfer or skateboarder”). [(surfing, skateboarding, slang) Synonym of gremlin (“a young or inexperienced surfer or skateboarder”).]