I’m thinking that August escaped the curse because he’s not been born yet in FTL, just like Henry is unborn since this mother is still an infant there. I’m imagining that FTL is currently asleep like when the field of poppies put all of Oz to sleep or when Malificent put the kingdom of Princess Aurora to sleep.
So Emma, Henry and August have not become as old as they are in SB because nothing is changing in FTL until the curse is broken. Having escaped the curse, that trio can break the curse in FTL and SB. I suspect that will require all three coming into their individual powers fully, much Dorothy’s companions did to cross the drawbridge into the Wicked Witch’s castle in Oz.