“Frantisek is young enough for Zofie” was not accepted. I know the meaning is different from “Frantisek is quite young for Zofie”. “Quite young” implies possibly too young. “Young enough” implies probably the appropriate age. What would be the right way to say “Frantisek is young enough for Zofie”? Does “dost” mean “quite” when it precedes an adjective and “enough” when it precedes a noun?
No, tyere is no such distinction (noun/pronoun). It means both enough (the original meaning) and quite. But sometimes only one of those meanings will be assumed by native speakers and you will have to say it differently for the other meaning.
František je pro Žofii dostatečně mladý.
František je pro Žofii mladý dost.