Adjective endings after “ein”-words are strong, which means that they typically indicate the gender of the nouns they modify in the nominative and accusative cases, but the dative and genitive case endings are all ‘en,’ leaving the question of gender on that basis alone ambiguous. In those cases, the “ein”-word takes on the strong ending (e.g. in dative singular feminine, “einer jungen Frau,” the indefinite article has an ‘er’ ending for dative feminine).
Here is a simpler table with just the adjective endings after the indefinite article:
Essentially, you only need to memorize the endings for nominative masculine, feminine, and neuter, as well as accusative feminine and neuter, as all others are ‘en.’