Not Lost Age, Lost Age is Golden Sun II. GSLA was always incompatible. If i remember correctly, first Golden Sun was playable in gpsp from repos, before two latest updates here. I think you can make something with game_config.txt, not with the core of emulator.
Also, if you would like to take a look at some changes, notaz seems to be still working on this emulator, there are neon scaling features, if you have the time to implement that as an option...