Try this age modifier code, it should keep you age frozen. I don't know if it works tho.
_V0 L Partner Age Modifier (0-99)
$0200 862FFAF4 0000000A
_V0 R Partner Age Modifier (0-99)
$0200 862FFD2C 0000000A
A digivolution code, as I suspected, wasn't on the table.So I'll have to make it...