"She asked about my age."
Translation:Ŝi demandis pri mia aĝo.
Only prepositions that can give both, location or direction, take the accusative for the direction. All others, including those who give a direction only, take no accusative.
Examples for location/direction:
en la domo – in the house (location)
en la domon – into the house (direction)
Direction, but no location can be given with that preposition:
al la domo – to the house (direction)
de la domo – from the house (direction)
Neither direction nor location:
pri la domo – about the house