Dwelling, fortified place, or castle
Derived from the Middle English and Old French word 'castel', which itself comes from the Latin 'castellum'. It originally referred to a fortified village or a large fortified residence. As a surname, it was often given to someone who lived in or near a castle, or worked in one.
Less common today
Castle isn't in the latest US Top 1000. It last peaked at #3,461 in 2018.
American child actor
The protagonist known as Ghost in the Track series Β· Ghost by Jason Reynolds
US births per 5-year period, 1990βpresent (SSA data).